Cancer-a life threatening diseas

Cancer begins when a cell breaks free from the normal restraints on cell division and begins to follow its own agenda for proliferation  All of the cells produced by division of this first, ancestral cell and its progeny also display inappropriate proliferation. A tumor, or mass of cells, formed of these abnormal cells may remain within the tissue in which it originated (a condition called in situ cancer), or it may begin to invade nearby tissues (a condition called invasive cancer). An invasive tumor is said to be malignant, and cells shed into the blood or lymph from a malignant tumor are likely to establish new tumors (metastases) throughout the body. Tumors threaten an individual’s life when their growth disrupts the tissues and organs needed for survival

figure 3

The stages of tumor development.

A malignant tumor develops across time, as shown in this diagram. This tumor develops as a result of four mutations, but the number of mutations involved in other types of tumors can vary. We do not know the exact number of mutations required for a normal cell to become a fully malignant cell, but the number is probably less than ten.

 a. The tumor begins to develop when a cell experiences a mutation that makes the cell more likely to divide than it normally would

b. The altered cell and its descendants grow and divide too often, a condition called hyperplasia. At some point, one of these cells experiences another mutation that further increases its tendency to divide

c. This cell’s descendants divide excessively and look abnormal, a condition called dysplasia. As time passes, one of the cells experiences yet another mutation. 

d. This cell and its descendants are very abnormal in both growth and appearance. If the tumor that has formed from these cells is still contained within its tissue of origin, it is called in situ cancer. In situ cancer may remain contained indefinitely. 

e. If some cells experience additional mutations that allow the tumor to invade neighboring tissues and shed cells into the blood or lymph, the tumor is said to be malignant. The escaped cells may establish new tumors (metastases) at other locations in the body.

Cancer is defined as any of a group of diseases in which particular cells in a body cease to respond to normal growth controls. The cells multiply unchecked, crowding out, invading, and destroying other tissues. One of the most important discoveries in cancer research in recent years are the genes that scientists think promote this unrestricted growth, called oncogenes. Experts believe that oncogenes alter receptor molecules located on the surface of cells that are responsible for signaling the cell to divide. These receptors somehow get stuck in the “on” position, sending signals to the cells to replicate at a rate that far exceeds cell loss.

Oncogenes and faulty receptors are certainly critical to the formation of cancerous tumors. Studies show, however, that the blood vessels that feed a growing tumor are just as important. Without a steady supply of oxygen and nutrients, cancerous tissues grow extremely slowly, are unable to spread throughout the body, or die out altogether.

The circulatory system must extend to all living tissues within the body. Therefore, wherever the body is undergoing development, growth, or repair, it must also grow a network of new blood vessels in a process called angiogenesis. Cancerous tissues are no different, although they promote angiogenesis somewhat indirectly. Tumor cells send chemical signals, called activator molecules, to the host’s healthy cells. These chemical signals activate genes in the healthy tissue that, in turn, encourage the growth of new blood vessels into and around the cancerous tissue.

Medical researchers are now using this knowledge in their search for a cure for cancer. In one study, injections of a protein called endostatin, known to inhibit angiogenesis, greatly reduced the number of cancer cells and the size of tumors in a group of laboratory mice. Whether or not similar drugs can safely prevent the growth and spread of cancer cells in humans has been the focus of dozens of ongoing clinical trials since the late 1990s. While cancer researchers are cautious with their predictions, they say that results of these trials may lead to successful treatments of some forms of cancer. 

Cancer harms the body when damaged cells divide uncontrollably to form lumps or masses of tissue called tumors (except in the case of leukemia where cancer prohibits normal blood function by abnormal cell division in the blood stream). Tumors can grow and interfere with the digestive, nervous, and circulatory systems, and they can release hormones that alter body function. Tumors that stay in one spot and demonstrate limited growth are generally considered to be benign.

Cancer cell

More dangerous, or malignant, tumors form when two things occur:

  1. a cancerous cell manages to move throughout the body using the blood or lymph systems, destroying healthy tissue in a process called invasion
  2. that cell manages to divide and grow, making new blood vessels to feed itself in a process called angiogenesis.

When a tumor successfully spreads to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasized. This process itself is called metastasis, and the result is a serious condition that is very difficult to treat.

In 2007, cancer claimed the lives of about 7.6 million people in the world. Physicians and researchers who specialize in the study, diagnosis, treatment, and prevention of cancer are called oncologists.

What causes cancer?

Cancer is ultimately the result of cells that uncontrollably grow and do not die. Normal cells in the body follow an orderly path of growth, division, and death. Programmed cell death is called apoptosis, and when this process breaks down, cancer begins to form. Unlike regular cells, cancer cells do not experience programmatic death and instead continue to grow and divide. This leads to a mass of abnormal cells that grows out of control.

Genes – the DNA type

Cells can experience uncontrolled growth if there are damages or mutations to DNA, and therefore, damage to the genes involved in cell division. Four key types of gene are responsible for the cell division process: oncogenes tell cells when to divide, tumor suppressor genes tell cells when not to divide, suicide genes control apoptosis and tell the cell to kill itself if something goes wrong, and DNA-repair genes instruct a cell to repair damaged DNA.

Cancer occurs when a cell’s gene mutations make the cell unable to correct DNA damage and unable to commit suicide. Similarly, cancer is a result of mutations that inhibit oncogene and tumor suppressor gene function, leading to uncontrollable cell growth.

What is a carcinogen?

Cancer is caused by changes in a cell’s DNA – its genetic “blueprint.” Some of these changes may be inherited from our parents, while others may be caused by outside exposures, which are often referred to as environmental factors. Environmental factors can include a wide range of exposures, such as:

  • Lifestyle factors (nutrition, tobacco use, physical activity, etc.)
  • Naturally occurring exposures (ultraviolet light, radon gas, infectious agents, etc.)
  • Medical treatments (chemotherapy, radiation, immune system-suppressing drugs, etc.)
  • Workplace exposures
  • Household exposures
  • Pollution

Substances and exposures that can lead to cancer are called carcinogens. Some carcinogens do not affect DNA directly, but lead to cancer in other ways. For example, they may cause cells to divide at a faster than normal rate, which could increase the chances that DNA changes will occur.

Carcinogens do not cause cancer in every case, all the time. Substances labeled as carcinogens may have different levels of cancer-causing potential. Some may cause cancer only after prolonged, high levels of exposure. And for any particular person, the risk of developing cancer depends on many factors, including how they are exposed to a carcinogen, the length and intensity of the exposure, and the person’s genetic makeup.

How do researchers determine if something is a carcinogen?

Testing to see if something can cause cancer is often difficult. It is not ethical to test a substance by exposing people to it and seeing if they get cancer from it. That’s why scientists must use other types of tests, which may not always give clear answers.

Lab studies

Scientists get much of their data about whether something might cause cancer from lab studies in cell cultures and animals. There are far too many substances (both natural and man-made) to test each one in lab animals, so scientists use what is already known about chemical structures, results from other types of lab tests, the extent of human exposure, and other factors to select chemicals for testing. For example, they can often get an idea about whether a substance might cause a problem by comparing it to similar chemicals that have already been studied.

Although lab studies alone can’t always predict if a substance will cause cancer in people, virtually all known human carcinogens that have been adequately tested also cause cancer in lab animals. In many cases, carcinogens are first found to cause cancer in lab animals and are later found to cause cancer in people.

Most studies of potential carcinogens expose the lab animals to doses that are much higher than common human exposures. This is so that cancer risk can be detected in relatively small groups of animals. It is not always clear if the results from animal studies will be the same for people as they are normally exposed to a substance. For example, the effects seen in lab studies with very high doses of a substance may not be the same at much lower doses, or the effects of a substance when it is inhaled may not be the same as if it is applied to the skin. Also, the bodies of lab animals and humans don’t always process substances in the same way.

But for safety reasons, it is usually assumed that exposures that cause cancer at larger doses in animals may also cause cancer in people. It isn’t always possible to know how the exposure dose might affect risk, but it is reasonable for public health purposes to assume that lowering human exposure will reduce risk.

Studies in people

Another important way to identify carcinogens is through epidemiologic studies, which look at human populations to determine which factors might be linked to cancer. These studies also provide useful information, but they have their limits. Humans do not live in a controlled environment. People are exposed to many substances at any given time, including those they encounter at work, school, or home; in the food they eat; and in the air they breathe. It’s very unlikely they know exactly what they’ve been exposed to or that they would be able to remember all of their exposures if asked by a researcher. And there are usually many years (often decades) between exposure to a carcinogen and the development of cancer. Therefore, it can be very hard to definitely link any particular exposure to cancer.

By combining data from both types of studies, scientists do their best to make an educated assessment of a substance’s cancer-causing ability. When the evidence is conclusive, the substance is labeled as a carcinogen. When the available evidence is compelling but not felt to be conclusive, the substance may be considered to be a probable carcinogen. But in some cases there simply isn’t enough information to be certain one way or the other.

Who determines how carcinogens are classified?

Several agencies (national and international) are responsible for determining the cancer-causing potential of different substances.

International Agency for Research on Cancer

The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). Its major goal is to identify causes of cancer. The most widely used system for classifying carcinogens comes from the IARC. In the past 30 years, the IARC has evaluated the cancer-causing potential of more than 900 likely candidates, placing them into one of the following groups:

  • Group 1: Carcinogenic to humans
  • Group 2A: Probably carcinogenic to humans
  • Group 2B: Possibly carcinogenic to humans
  • Group 3: Unclassifiable as to carcinogenicity in humans
  • Group 4: Probably not carcinogenic to humans

Perhaps not surprisingly, based on how hard it can be to test these candidate carcinogens, most are listed as being of probable, possible, or unknown risk. Only a little over 100 are classified as “carcinogenic to humans.”

National Toxicology Program

The National Toxicology Program (NTP) is formed from parts of several different US government agencies, including the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). The NTP updates its Report on Carcinogens (RoC) every few years.

The Report on Carcinogens identifies 2 groups of agents:

  • “Known to be human carcinogens”
  • “Reasonably anticipated to be human carcinogens”

The current version of the RoC lists about 240 substances and exposures. Unlike the IARC’s list, the RoC does not list substances that have been studied and found not to be carcinogens.

Environmental Protection Agency

The US Environmental Protection Agency (EPA) maintains the Integrated Risk Information System (IRIS), an electronic database that contains information on human health effects from exposure to certain substances in the environment. The EPA uses a rating system similar to that of IARC when describing the cancer-causing potential of a substance:

  • Group A: Carcinogenic to humans
  • Group B: Likely to be carcinogenic to humans
  • Group C: Suggestive evidence of carcinogenic potential
  • Group D: Inadequate information to assess carcinogenic potential
  • Group E: Not likely to be carcinogenic to humans

Other agencies and groups

Other federal agencies, such as the CDC’s National Institute for Occupational Safety and Health (NIOSH), the Food and Drug Administration (FDA), and the National Cancer Institute may comment on whether a substance or exposure may cause cancer and/or what levels of exposure to a particular substance might be considered acceptable.

Some state agencies also keep lists of known or probable carcinogens. For example, the California Environmental Protection Agency (CalEPA) maintains a list of “chemicals known to the state to cause cancer or reproductive toxicity.” (Much of this list is based on the IARC and NTP lists below.)

The American Cancer Society’s role

The American Cancer Society (ACS) contributes in many ways to evaluating how environmental factors affect a person’s likelihood of developing cancer, including:

  • Conducting epidemiologic research on the causes of cancer
  • Funding laboratory and epidemiologic research at universities and other institutions that study environmental causes of cancer
  • Advocating for environmental health on a local, state, and federal level
  • Informing the public about environmental factors that affect cancer risk and how to decrease their risk of developing cancer

In most cases, the ACS does not directly evaluate whether a certain substance or exposure causes cancer. Instead, the ACS looks to national and international organizations such as the NTP and IARC, whose mission is to evaluate environmental cancer risks based on evidence from laboratory and human research studies.

Some important points about the IARC and NTP lists here

The IARC and NTP act independently but have studied many of the same agents, so many known or suspected carcinogens appear on both lists. But because an agent appears on one and not on the other does not necessarily mean there is a controversy, as one agency may not have evaluated it.

Unfortunately, many of the substances and exposures on the lists below can often go by different names. This can make it hard to find a particular substance on one or both of these lists, which are in alphabetical order and may not always use the most common term.

These lists include only those agents that have been evaluated by the agencies. These agencies tend to focus on substances and exposures most likely to cause cancer, but there are many others that have not been studied fully yet.

Most of the agents on the lists have been linked only with certain kinds of cancer, not all types. For more detailed information, refer to the specific monographs or reports published by the agencies (available on their Web sites).

The lists themselves say nothing about how likely it is that an agent will cause cancer. Carcinogens do not cause cancer at all times, under all circumstances. Some may only be carcinogenic if a person is exposed in a certain way (for example, swallowing it as opposed to touching it). Some may only cause cancer in people who have a certain genetic makeup. Some of these agents may lead to cancer after only a very small exposure, while others might require intense exposure over many years. Again, you should refer to the agencies’ reports for specifics.

Even if a substance or exposure is known or suspected to cause cancer, this does not necessarily mean that it can or should be avoided at all costs. For example, exposure to ionizing radiation is known to cause cancer, with increased risks even at low levels of exposure. Yet there is no way to completely prevent exposure to natural sources of radiation such as cosmic radiation from the sun or radon in soil. These lists also include many commonly used medicines, particularly some hormones and drugs used to treat cancer. For example, tamoxifen increases the risk of certain kinds of uterine cancer but can be very useful in treating some breast cancers, which may be more important for some women. If you have questions about a medicine that appears on one of these lists, be sure to ask your doctor.

Looking at the list below can tell you whether or not something may increase your risk of cancer, but it is important to try to get an idea of how much it might increase your risk. It is also important to know what your risk is to begin with. Many factors can enter into this, including your age, gender, family history, and lifestyle factors (tobacco and alcohol use, weight, diet, physical activity level, etc.). As noted above, the type and extent of exposure to a substance may also play a role. You should consider the actual amount of increased risk when deciding if you should limit or avoid an exposure.

Known human carcinogens

International Agency for Research on Cancer
Group 1: Carcinogenic to humans

  • Acetaldehyde (from consuming alcoholic beverages)
  • Acid mists, strong inorganic
  • Aflatoxins
  • Alcoholic beverages
  • Aluminum production
  • 4-Aminobiphenyl
  • Areca nut
  • Aristolochic acid (and plants containing it)
  • Arsenic and inorganic arsenic compounds
  • Asbestos (all forms) and mineral substances (such as talc or vermiculite) that contain asbestos
  • Auramine production
  • Azathioprine
  • Benzene
  • Benzidine and dyes metabolized to benzidine
  • Benzo[a]pyrene
  • Beryllium and beryllium compounds
  • Betel quid, with or without tobacco
  • Bis(chloromethyl)ether and chloromethyl methyl ether (technical-grade)
  • Busulfan
  • 1,3-Butadiene
  • Cadmium and cadmium compounds
  • Chlorambucil
  • Chlornaphazine
  • Chromium (VI) compounds
  • Clonorchis sinensis (infection with)
  • Coal, indoor emissions from household combustion
  • Coal gasification
  • Coal-tar distillation
  • Coal-tar pitch
  • Coke production
  • Cyclophosphamide
  • Cyclosporine
  • Diethylstilbestrol
  • Epstein-Barr virus (infection with)
  • Erionite
  • Estrogen postmenopausal therapy
  • Estrogen-progestogen postmenopausal therapy (combined)
  • Estrogen-progestogen oral contraceptives (combined) (Note: There is also convincing evidence in humans that these agents confer a protective effect against cancer in the endometrium and ovary)
  • Ethanol in alcoholic beverages
  • Ethylene oxide
  • Etoposide
  • Etoposide in combination with cisplatin and bleomycin
  • Fission products, including strontium-90
  • Formaldehyde
  • Haematite mining (underground)
  • Helicobacter pylori (infection with)
  • Hepatitis B virus (chronic infection with)
  • Hepatitis C virus (chronic infection with)
  • Human immunodeficiency virus type 1 (HIV-1) (infection with)
  • Human papilloma virus (HPV) types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 (infection with) (Note: The HPV types that have been classified as carcinogenic to humans can differ by an order of magnitude in risk for cervical cancer)
  • Human T-cell lymphotropic virus type I (HTLV-1) (infection with)
  • Ionizing radiation (all types)
  • Iron and steel founding (workplace exposure)
  • Isopropyl alcohol manufacture using strong acids
  • Kaposi sarcoma herpesvirus (KSHV)/human herpesvirus 8 (HHV-8) (infection with)
  • Leather dust
  • Magenta production
  • Melphalan
  • Methoxsalen (8-methoxypsoralen) plus ultraviolet A radiation
  • 4,4′-Methylenebis(chloroaniline) (MOCA)
  • Mineral oils, untreated or mildly treated
  • MOPP and other combined chemotherapy including alkylating agents
  • 2-Naphthylamine
  • Neutron radiation
  • Nickel compounds
  • N’-Nitrosonornicotine (NNN) and 4-(N-Nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK)
  • Opisthorchis viverrini (liver fluke; infection with)
  • Painter (workplace exposure as a)
  • 3,4,5,3′,4′-Pentachlorobiphenyl (PCB-126)
  • 2,3,4,7,8-Pentachlorodibenzofuran
  • Phenacetin (and mixtures containing it)
  • Phosphorus-32, as phosphate
  • Plutonium
  • Radioiodines, including iodine-131
  • Radionuclides, alpha-particle-emitting, internally deposited (Note: Specific radionuclides for which there is sufficient evidence for carcinogenicity to humans are also listed individually as Group 1 agents)
  • Radionuclides, beta-particle-emitting, internally deposited (Note: Specific radionuclides for which there is sufficient evidence for carcinogenicity to humans are also listed individually as Group 1 agents)
  • Radium-224 and its decay products
  • Radium-226 and its decay products
  • Radium-228 and its decay products
  • Radon-222 and its decay products
  • Rubber manufacturing industry
  • Salted fish (Chinese-style)
  • Schistosoma haematobium (flatworm; infection with)
  • Semustine (methyl-CCNU)
  • Shale oils
  • Silica dust, crystalline, in the form of quartz or cristobalite
  • Solar radiation
  • Soot (as found in workplace exposure of chimney sweeps)
  • Sulfur mustard
  • Tamoxifen (Note: There is also conclusive evidence that tamoxifen reduces the risk of contralateral breast cancer in breast cancer patients)
  • 2,3,7,8-Tetrachlorodibenzo-para-dioxin
  • Thiotepa
  • Thorium-232 and its decay products
  • Tobacco, smokeless
  • Tobacco smoke, secondhand
  • Tobacco smoking
  • ortho-Toluidine
  • Treosulfan
  • Ultraviolet (UV) radiation, including UVA, UVB, and UVC rays
  • Ultraviolet-emitting tanning devices
  • Vinyl chloride
  • Wood dust
  • X- and Gamma-radiation

National Toxicology Program 12th Report on Carcinogens
“Known to be human carcinogens”

  • Aflatoxins
  • Alcoholic beverage consumption
  • 4-Aminobiphenyl
  • Analgesic mixtures containing phenacetin
  • Aristolochic acids
  • Arsenic compounds, inorganic
  • Asbestos
  • Azathioprine
  • Benzene
  • Benzidine
  • Beryllium and beryllium compounds
  • 1,3-Butadiene
  • 1,4-Butanediol dimethylsulfonate (busulfan, Myleran®)
  • Cadmium and cadmium compounds
  • Chlorambucil
  • 1-(2-Chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea (MeCCNU)
  • bis(chloromethyl) ether and technical-grade chloromethyl methyl ether
  • Chromium hexavalent compounds
  • Coal tar pitches
  • Coal tars
  • Coke oven emissions
  • Cyclophosphamide
  • Cyclosporin A
  • Diethylstilbestrol (DES)
  • Dyes metabolized to benzidine
  • Environmental tobacco smoke
  • Erionite
  • Estrogens, steroidal
  • Ethylene oxide
  • Formaldehyde
  • Hepatitis B virus
  • Hepatitis C virus
  • Human papilloma viruses: some genital-mucosal types
  • Melphalan
  • Methoxsalen with ultraviolet A therapy (PUVA)
  • Mineral oils (untreated and mildly treated)
  • Mustard gas
  • 2-Naphthylamine
  • Neutrons
  • Nickel compounds
  • Oral tobacco products
  • Radon
  • Silica, crystalline (respirable size)
  • Solar radiation
  • Soots
  • Strong inorganic acid mists containing sulfuric acid
  • Sunlamps or sunbeds, exposure to
  • Tamoxifen
  • 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD); “dioxin”
  • Thiotepa
  • Thorium dioxide
  • Tobacco smoking
  • Vinyl chloride
  • Ultraviolet radiation, broad spectrum UV radiation
  • Wood dust
  • X-radiation and gamma radiation

Probable carcinogens

International Agency for Research on Cancer 
Group 2A: Probably carcinogenic to humans

  • Acrylamide
  • Adriamycin (doxorubicin)
  • Androgenic (anabolic) steroids
  • Art glass, glass containers, and press ware (manufacture of)
  • Azacitidine
  • Biomass fuel (primarily wood), emissions from household combustion
  • Bischloroethyl nitrosourea (BCNU)
  • Captafol
  • Carbon electrode manufacture
  • Chloramphenicol
  • alpha-Chlorinated toluenes (benzal chloride, benzotrichloride, benzyl chloride) and benzoyl chloride (combined exposures)
  • 1-(2-Chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU)
  • 4-Chloro-ortho-toluidine
  • Chlorozotocin
  • Cisplatin
  • Cobalt metal with tungsten carbide
  • Creosotes
  • Cyclopenta[cd]pyrene
  • Dibenz[a,h]anthracene
  • Dibenzo[a,l]pyrene
  • Diethyl sulfate
  • Dimethylcarbamoyl chloride
  • 1,2-Dimethylhydrazine
  • Dimethyl sulfate
  • Engine exhaust, diesel
  • Epichlorohydrin
  • Ethyl carbamate (urethane)
  • Ethylene dibromide
  • N-Ethyl-N-nitrosourea
  • Frying, emissions from high-temperature
  • Glycidol
  • Hairdresser or barber (workplace exposure as)
  • Human papillomavirus (HPV) type 68 (infection with)
  • Indium phosphide
  • IQ (2-Amino-3-methylimidazo[4,5-f]quinoline)
  • Lead compounds, inorganic
  • Mate, hot
  • 5-Methoxypsoralen
  • Methyl methanesulfonate
  • N-Methyl-N´-nitro-N-nitrosoguanidine (MNNG)
  • N-Methyl-N-nitrosourea
  • Nitrate or nitrite (ingested) under conditions that result in endogenous nitrosation
  • Nitrogen mustard
  • N-Nitrosodiethylamine
  • N-Nitrosodimethylamine
  • 2-Nitrotoluene
  • Non-arsenical insecticides (workplace exposures in spraying and application of)
  • Petroleum refining (workplace exposures in)
  • Polychlorinated biphenyls (PCBs)
  • Procarbazine hydrochloride
  • Shiftwork that involves circadian disruption
  • Styrene-7,8-oxide
  • Teniposide
  • Tetrachloroethylene (perchloroethylene)
  • Trichloroethylene
  • 1,2,3-Trichloropropane
  • Tris(2,3-dibromopropyl) phosphate
  • Vinyl bromide (Note: For practical purposes, vinyl bromide should be considered to act similarly to the human carcinogen vinyl chloride.)
  • Vinyl fluoride (Note: For practical purposes, vinyl fluoride should be considered to act similarly to the human carcinogen vinyl chloride.)

National Toxicology Program 12th Report on Carcinogens
“Reasonably anticipated to be human carcinogens”

  • Acetaldehyde
  • 2-Acetylaminofluorene
  • Acrylamide
  • Acrylonitrile
  • Adriamycin® (doxorubicin hydrochloride)
  • 2-Aminoanthraquinone
  • o-Aminoazotoluene
  • 1-Amino-2,4-dibromoanthraquinone
  • 1-Amino-2-methylanthraquinone
  • 2-Amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ)
  • 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)
  • 2-Amino-3-methylimidazo[4,5-f]quinoline (IQ)
  • 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)
  • Amitrole
  • o-Anisidine hydrochloride
  • Azacitidine (5-Azacytidine®, 5-AzaC)
  • Benz[a]anthracene
  • Benzo[b]fluoranthene
  • Benzo[j]fluoranthene
  • Benzo[k]fluoranthene
  • Benzo[a]pyrene
  • Benzotrichloride
  • Bromodichloromethane
  • 2, 2-bis-(bromoethyl)-1,3-propanediol (technical grade)
  • Butylated hydroxyanisole (BHA)
  • Captafol
  • Carbon tetrachloride
  • Ceramic fibers (respirable size)
  • Chloramphenicol
  • Chlorendic acid
  • Chlorinated paraffins (C12, 60% chlorine)
  • 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea
  • Bis(chloroethyl) nitrosourea
  • Chloroform
  • 3-Chloro-2-methylpropene
  • 4-Chloro-o-phenylenediamine
  • Chloroprene
  • p-Chloro-o-toluidine and p-chloro-o-toluidine hydrochloride
  • Chlorozotocin
  • C.I. basic red 9 monohydrochloride
  • Cisplatin
  • Cobalt sulfate
  • Cobalt-tungsten carbide: powders and hard metals
  • p-Cresidine
  • Cupferron
  • Dacarbazine
  • Danthron (1,8-dihydroxyanthraquinone)
  • 2,4-Diaminoanisole sulfate
  • 2,4-Diaminotoluene
  • Diazoaminobenzene
  • Dibenz[a,h]acridine
  • Dibenz[a,j]acridine
  • Dibenz[a,h]anthracene
  • 7H-Dibenzo[c,g]carbazole
  • Dibenzo[a,e]pyrene
  • Dibenzo[a,h]pyrene
  • Dibenzo[a,i]pyrene
  • Dibenzo[a,l]pyrene
  • 1,2-Dibromo-3-chloropropane
  • 1,2-Dibromoethane (ethylene dibromide)
  • 2,3-Dibromo-1-propanol
  • Tris (2,3-dibromopropyl) phosphate
  • 1,4-Dichlorobenzene
  • 3,3′-Dichlorobenzidine and 3,3′-dichlorobenzidine dihydrochloride
  • Dichlorodiphenyltrichloroethane (DDT)
  • 1,2-Dichloroethane (ethylene dichloride)
  • Dichloromethane (methylene chloride)
  • 1,3-Dichloropropene (technical grade)
  • Diepoxybutane
  • Diesel exhaust particulates
  • Diethyl sulfate
  • Diglycidyl resorcinol ether
  • 3,3′-Dimethoxybenzidine
  • 4-Dimethylaminoazobenzene
  • 3,3′-Dimethylbenzidine
  • Dimethylcarbamoyl chloride
  • 1,1-Dimethylhydrazine
  • Dimethyl sulfate
  • Dimethylvinyl chloride
  • 1,6-Dinitropyrene
  • 1,8-Dinitropyrene
  • 1,4-Dioxane
  • Disperse blue 1
  • Dyes metabolized to 3,3′-dimethoxybenzidine
  • Dyes metabolized to 3,3′-dimethylbenzidine
  • Epichlorohydrin
  • Ethylene thiourea
  • Di(2-ethylhexyl) phthalate
  • Ethyl methanesulfonate
  • Furan
  • Glass wool fibers (inhalable)
  • Glycidol
  • Hexachlorobenzene
  • Hexachlorocyclohexane isomers
  • Hexachloroethane
  • Hexamethylphosphoramide
  • Hydrazine and hydrazine sulfate
  • Hydrazobenzene
  • Indeno[1,2,3-cd]pyrene
  • Iron dextran complex
  • Isoprene
  • Kepone® (chlordecone)
  • Lead and lead compounds
  • Lindane and other hexachlorocyclohexane isomers
  • 2-Methylaziridine (propylenimine)
  • 5-Methylchrysene
  • 4,4′-Methylenebis(2-chloroaniline)
  • 4-4′-Methylenebis(N,N-dimethyl)benzenamine
  • 4,4′-Methylenedianiline and its dihydrochloride salt
  • Methyleugenol
  • Methyl methanesulfonate
  • N-methyl-N’-nitro-N-nitrosoguanidine
  • Metronidazole
  • Michler’s ketone [4,4′-(dimethylamino) benzophenone]
  • Mirex
  • Naphthalene
  • Nickel (metallic)
  • Nitrilotriacetic acid
  • o-Nitroanisole
  • Nitrobenzene
  • 6-Nitrochrysene
  • Nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether)
  • Nitrogen mustard hydrochloride
  • Nitromethane
  • 2-Nitropropane
  • 1-Nitropyrene
  • 4-Nitropyrene
  • N-nitrosodi-n-butylamine
  • N-nitrosodiethanolamine
  • N-nitrosodiethylamine
  • N-nitrosodimethylamine
  • N-nitrosodi-n-propylamine
  • N-nitroso-N-ethylurea
  • 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone
  • N-nitroso-N-methylurea
  • N-nitrosomethylvinylamine
  • N-nitrosomorpholine
  • N-nitrosonornicotine
  • N-nitrosopiperidine
  • N-nitrosopyrrolidine
  • N-nitrososarcosine
  • o-Nitrotoluene
  • Norethisterone
  • Ochratoxin A
  • 4,4′-Oxydianiline
  • Oxymetholone
  • Phenacetin
  • Phenazopyridine hydrochloride
  • Phenolphthalein
  • Phenoxybenzamine hydrochloride
  • Phenytoin
  • Polybrominated biphenyls (PBBs)
  • Polychlorinated biphenyls (PCBs)
  • Polycyclic aromatic hydrocarbons (PAHs)
  • Procarbazine hydrochloride
  • Progesterone
  • 1,3-Propane sultone
  • beta-Propiolactone
  • Propylene oxide
  • Propylthiouracil
  • Reserpine
  • Riddelliine
  • Safrole
  • Selenium sulfide
  • Streptozotocin
  • Styrene
  • Styrene-7,8-oxide
  • Sulfallate
  • Tetrachloroethylene (perchloroethylene)
  • Tetrafluoroethylene
  • Tetranitromethane
  • Thioacetamide
  • 4,4′-Thiodianaline
  • Thiourea
  • Toluene diisocyanate

Genes – the family type

Cancer can be the result of a genetic predisposition that is inherited from family members. It is possible to be born with certain genetic mutations or a fault in a gene that makes one statistically more likely to develop cancer later in life.

Other medical factors

As we age, there is an increase in the number of possible cancer-causing mutations in our DNA. This makes age an important risk factor for cancer. Several viruses have also been linked to cancer such as: human papillomavirus (a cause of cervical cancer), hepatitis B and C (causes of liver cancer), and Epstein-Barr virus (a cause of some childhood cancers). Human immunodeficiency virus (HIV) – and anything else that suppresses or weakens the immune system – inhibits the body’s ability to fight infections and increases the chance of developing cancer.

What are the symptoms of cancer?

Cancer symptoms are quite varied and depend on where the cancer is located, where it has spread, and how big the tumor is. Some cancers can be felt or seen through the skin – a lump on the breast or testicle can be an indicator of cancer in those locations. Skin cancer (melanoma) is often noted by a change in a wart or mole on the skin. Some oral cancers present white patches inside the mouth or white spots on the tongue.

Other cancers have symptoms that are less physically apparent. Some brain tumors tend to present symptoms early in the disease as they affect important cognitive functions. Pancreas cancers are usually too small to cause symptoms until they cause pain by pushing against nearby nerves or interfere with liver function to cause a yellowing of the skin and eyes called jaundice. Symptoms also can be created as a tumor grows and pushes against organs and blood vessels. For example, colon cancers lead to symptoms such as constipation, diarrhea, and changes in stool size. Bladder or prostate cancers cause changes in bladder function such as more frequent or infrequent urination.

As cancer cells use the body’s energy and interfere with normal hormone function, it is possible to present symptoms such as fever, fatigue, excessive sweating, anemia, and unexplained weight loss. However, these symptoms are common in several other maladies as well. For example, coughing and hoarseness can point to lung or throat cancer as well as several other conditions.

When cancer spreads, or metastasizes, additional symptoms can present themselves in the newly affected area. Swollen or enlarged lymph nodes are common and likely to be present early. If cancer spreads to the brain, patients may experience vertigo, headaches, or seizures. Spreading to the lungs may cause coughing and shortness of breath. In addition, the liver may become enlarged and cause jaundice and bones can become painful, brittle, and break easily. Symptoms of metastasis ultimately depend on the location to which the cancer has spread.

How is cancer classified?

There are five broad groups that are used to classify cancer.

  1. Carcinomas are characterized by cells that cover internal and external parts of the body such as lung, breast, and colon cancer.
  2. Sarcomas are characterized by cells that are located in bone, cartilage, fat, connective tissue, muscle, and other supportive tissues.
  3. Lymphomas are cancers that begin in the lymph nodes and immune system tissues.
  4. Leukemias are cancers that begin in the bone marrow and often accumulate in the bloodstream.
  5. Adenomas are cancers that arise in the thyroid, the pituitary gland, the adrenal gland, and other glandular tissues.

Cancers are often referred to by terms that contain a prefix related to the cell type in which the cancer originated and a suffix such as -sarcoma, -carcinoma, or just -oma. Common prefixes include:

  • Adeno- = gland
  • Chondro- = cartilage
  • Erythro- = red blood cell
  • Hemangio- = blood vessels
  • Hepato- = liver
  • Lipo- = fat
  • Lympho- = white blood cell
  • Melano- = pigment cell
  • Myelo- = bone marrow
  • Myo- = muscle
  • Osteo- = bone
  • Uro- = bladder
  • Retino- = eye
  • Neuro- = brain

Cancer Diagnosis

How is cancer diagnosed?

There is no single test that can accurately diagnose cancer. The complete evaluation of a patient usually requires a thorough history and physical examination along with diagnostic testing. Many tests are needed to determine whether a person has cancer, or if another condition (such as an infection) is mimicking the symptoms of cancer.

Effective diagnostic testing is used to confirm or eliminate the presence of disease, monitor the disease process, and to plan for and evaluate the effectiveness of treatment. In some cases, it is necessary to repeat testing when a person’s condition has changed, if a sample collected was not of good quality, or an abnormal test result needs to be confirmed.

Diagnostic procedures for cancer may include imaging, laboratory tests (including tests for tumor markers), tumor biopsy, endoscopic examination, surgery, or genetic testing.

What are the different types of laboratory tests?

Clinical chemistry uses chemical processes to measure levels of chemical components in body fluids and tissues. The most common specimens used in clinical chemistry are blood and urine.

Many different tests exist to detect and measure almost any type of chemical component in blood or urine. Components may include blood glucose, electrolytes, enzymes, hormones, lipids (fats), other metabolic substances, and proteins.

The following are some of the more common laboratory tests:

  • blood tests
    A variety of blood tests are used to check the levels of substances in the blood that indicate how healthy the body is and whether infection is present. For example, blood tests revealing elevated levels of waste products, such as creatinine or blood urea nitrogen (BUN), indicate that the kidneys are not working efficiently to filter those substances out. Other tests check the presence of electrolytes – chemical compounds such as sodium and potassium that are critical to the body’s healthy functioning. Coagulation studies determine how quickly the blood clots.

    A complete blood count (CBC) measures the size, number, and maturity of the different blood cells in a specific volume of blood. This is one of the most common tests performed. Red blood cells are important for carrying oxygen and fighting anemia and fatigue; the hemoglobin portion of the CBC measures the oxygen carrying capacity of the red blood cells while the hematocrit measures the percentage of red blood cells in the blood. White blood cells fight infection. Increased numbers of white blood cells, therefore, may indicate the presence of an infection. Platelets prevent the body from bleeding and bruising easily.

  • urinalysis
    Urinalysis breaks down the components of urine to check for the presence of drugs, blood, protein, and other substances. Blood in the urine (hematuria) may be the result of a benign (noncancerous) condition, but it can also indicate an infection or other problem. High levels of protein in the urine (proteinuria) may indicate a kidney or cardiovascular problem.
  • tumor markers
    Tumor markers are substances either released by cancer cells into the blood or urine or substances created by the body in response to cancer cells. Tumor markers are used to evaluate how well a patient has responded to treatment and to check for tumor recurrence. Research is currently being conducted on the role of tumor markers in detection, diagnosis, and treatment of cancers.

    According to the National Cancer Institute (NCI), tumor markers are useful in identifying potential problems, but they must be used with other tests for the following reasons:

    • People with benign conditions may also have elevated levels of these substances in their blood.
    • Not every person with a tumor has tumor markers.
    • Some tumor markers are not specific to any one type of tumor.

The following is a brief description of some of the more useful tumor markers:

  • prostate-specific antigen (PSA)
    Prostate-specific antigen is always present in low concentrations in the blood of adult males. An elevated PSA level in the blood may indicate prostate cancer, but other conditions such as benign prostatic hyperplasia (BPH) and prostatitis can also raise PSA levels. PSA levels are used to evaluate how a patient has responded to treatment and to check for tumor recurrence.
  • prostatic acid phosphatase (PAP)
    PAP originates in the prostate and is normally present in small amounts in the blood. In addition to prostate cancer, elevated levels of PAP may indicate testicular cancer, leukemia, and non-Hodgkin’s lymphoma, as well as some noncancerous conditions.
  • CA 125
    Ovarian cancer is the most common cause of elevated CA 125, but cancers of the uterus, cervix, pancreas, liver, colon, breast, lung, and digestive tract can also raise CA 125 levels. Several noncancerous conditions can also elevate CA 125. CA 125 is mainly used to monitor the treatment of ovarian cancer.
  • carcinoembryonic antigen (CEA)
    CEA is normally found in small amounts in the blood. Colorectal cancer is the most common cancer that raises this tumor marker. Several other cancers can also raise levels of carcinoembryonic antigen.
  • alpha-fetoprotein (AFP)
    Alpha-fetoprotein is normally elevated in pregnant women since it is produced by the fetus. However, AFP is not usually found in the blood of adults. In men, and in women who are not pregnant, an elevated level of AFP may indicate liver cancer or cancer of the ovary or testicle. Noncancerous conditions may also cause elevated AFP levels.
  • human chorionic gonadotropin (HCG)
    HCG is another substance that appears normally in pregnancy and is produced by the placenta. If pregnancy is ruled out, HCG may indicate cancer in the testis, ovary, liver, stomach, pancreas, and lung. Marijuana use can also raise HCG levels.
  • CA 19-9
    This marker is associated with cancers in the colon, stomach, and bile duct. Elevated levels of CA 19-9 may indicate advanced cancer in the pancreas, but it is also associated with noncancerous conditions, including gallstones, pancreatitis, cirrhosis of the liver, and cholecystitis.
  • CA 15-3
    This marker is most useful in evaluating the effect of treatment for women with advanced breast cancer. Elevated levels of CA 15-3 are also associated with cancers of the ovary, lung, and prostate, as well as noncancerous conditions such as benign breast or ovarian disease, endometriosis, pelvic inflammatory disease, and hepatitis. Pregnancy and lactation also can raise CA 15-3 levels.
  • CA 27-29
    This marker, like CA 15-3, is used to follow the course of treatment in women with advanced breast cancer. Cancers of the colon, stomach, kidney, lung, ovary, pancreas, uterus, and liver may also raise CA 27-29 levels. Noncancerous conditions associated with this substance are first trimester pregnancy, endometriosis, ovarian cysts, benign breast disease, kidney disease, and liver disease.
  • lactate dehydrogenase (LDH)
    LDH is a protein that normally appears throughout the body in small amounts. Many cancers can raise LDH levels, so it is not useful in identifying a specific kind of cancer. Measuring LDH levels can be helpful in monitoring treatment for cancer. Noncancerous conditions that can raise LDH levels include heart failure, hypothyroidism, anemia, and lung or liver disease.
  • neuron-specific enolase (NSE)
    NSE is associated with several cancers, but it is used most often to monitor treatment in patients with neuroblastoma or small cell lung cancer.


    Treatment varies based on the type of cancer and its stage. The stage of a cancer refers to how much it has grown and whether the tumor has spread from its original location.

    • If the cancer is confined to one location and has not spread, the most common treatment approach is surgery to cure the cancer. This is often the case with skin cancers, as well as cancers of the lung, breast, and colon.

    • If the tumor has spread to local lymph nodes only, sometimes these can be removed.

    • If surgery cannot remove all of the cancer, the options for treatment include radiation, chemotherapy, or both. Some cancers require a combination of surgery, radiation, and chemotherapy.

    • Lymphoma, or cancer of the lymph glands, is rarely treated with surgery. Chemotherapy and radiation therapy are most often used to treat lymphoma.

    Although treatment for cancer can be difficult, there are many ways to keep up your strength.

    If you have radiation treatment, know that:

    • Radiation treatment is painless.

    • Treatment is usually scheduled every weekday.

    • You should allow 30 minutes for each treatment session, although the treatment itself usually takes only a few minutes.

    • You should get plenty of rest and eat a well-balanced diet during the course of your radiation therapy.

    • Skin in the treated area may become sensitive and easily irritated.

    • Side effects of radiation treatment are usually temporary. They vary depending on the area of the body that is being treated.

    If you are going through chemotherapy, you should eat right. Chemotherapy causes your immune system to weaken, so you should avoid people with colds or the flu. You should also get plenty of rest, and don’t feel as though you have to accomplish tasks all at once.

    It will help you to talk with family, friends, or a support group about your feelings. Work with your health care providers throughout your treatment. Helping yourself can make you feel more in control.

Source by ishit r kothari

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