Most solid tumours take ten to forty years after the first hit
Carcinogens—chemicals, radiation, viruses, bacteria—nudge cells toward cancer, usually by mutating DNA. For many solid tumours the lag between exposure and disease stretches a decade to four. Blood cancers can surface in as little as two years, which is why pinning blame is hard.
Any agent that promotes cancer counts, whether synthetic chemical, natural substance, radiation, or microbe; the fungal toxin aflatoxin B1 in stored grain causes liver cancer, and H. pylori bacteria cause stomach cancer. Chemically, agents split into activation-dependent types that the body must metabolise into DNA-reactive forms, and activation-independent direct-acting ones such as ultraviolet light, ionizing radiation, and certain alkylators that attack DNA as they are. The WHO's International Agency for Research on Cancer, set up in 1965 in Lyon, has issued monographs since 1971 that rank agents from Group 1, carcinogenic to humans, down to Group 4, probably not.
Because workers meet rare chemicals at high, steady doses, much of the proof for specific agents comes from occupational studies. Everyday exposures include sunlight UV, basement radon, pollutants, cigarette smoke, alcohol, and cured meats whose nitrites draw concern for colon cancer links without proven causation. Occupational contact alone is estimated to kill about 666,000 people yearly worldwide. Alcohol drives tumours of head and neck, esophagus, liver, colon, rectum, and breast, and amplifies tobacco's damage; in the United States it accounts for roughly six percent of cancers and four percent of cancer deaths.
Not every wave on the spectrum is dangerous: radio, microwave, infrared, and visible light lack energy to break bonds, and food irradiated with electrons or X-rays is not itself carcinogenic. Ultraviolet sun exposure remains the leading cause of skin cancer; in Australia melanoma is the most common cancer diagnosed between ages fifteen and forty-four among pale-skinned people under strong sun. Cooking adds its own risks: grilling or barbecuing meat can form traces of benzo[a]pyrene, the same kind of potent compound found in cigarette smoke, which itself carries at least 70 known carcinogens.
Source: Carcinogen
