carcinogen - IARC classification of carcinogens

An agent which is capable of inducing cancer in tissues exposed to it. Several carcinogens have been identified by studies of the frequency of specific tumours in relation to different occupations, lifestyles, exposure to injurious chemical agents, drugs, ionizing radiations, ultraviolet light, and certain tumour-inducing (oncogenic) viruses. Exposure to such agents does not cause cancer immediately, but only after a period which may be months or years. The dose or duration of exposure to the agent is also critical: an example is cancer of the lung and cigarette smoking, where both the duration of smoking and the number of cigarettes smoked increase the probability of developing lung cancer some time in the future.

In pathology, a carcinogen is any substance or agent that promotes cancer.

Carcinogens may cause cancer by altering cellular metabolism or damaging DNA directly in cells, which interferes with normal biological processes.

Cooking protein-rich food at high temperatures, such as broiling or barbecuing meats, can lead to the formation of many potent carcinogens that are comparable to those found in cigarrette smoke (i.e., benzo[a]pyrene).

Benzene, kepone, EDB, asbestos, and the waste rock of oil-shale mining have all been classified as carcinogenic. Certain viruses such as Hepatitis B and human papilloma viruses have been found to cause cancer in humans.

CERCLA identifies all radionuclides as carcinogens, although the nature of the emitted radiation (alpha, beta, or gamma, and the energy), its consequent capacity to cause ionization in tissues, and the magnitude of radiation exposure, determine the potential hazard. For example, Thorotrast, an (incidentally-radioactive) suspension previously used as a contrast medium in x-ray diagnostics, is thought by some to be the most potent human carcinogen known because of its retention within various organs and persistent emission of alpha particles.

Recent reports have implicated acrylamide in fried or overheated carbohydrate foods (such as french fries and potato chips) as a possible carcinogen.

Co-carcinogens are chemicals which do not separately cause cancer, but do so in specific combinations.

IARC classification of carcinogens

Group 1: the agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans. Group 2A: the agent (mixture) is probably carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans. Group 2B: the agent (mixture) is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans. Group 3: the agent (mixture or exposure circumstance) is not classifiable as to its carcinogenicity to humans. Group 4: the agent (mixture) is probably not carcinogenic to humans.