Multiple primary cancer and its risk factors in the Aichi Cancer Registry.

To elucidate the risk factors of multiple primary cancer a case-control analysis was performed on 265 cases of multiple primary cancer (a total of 490 cancers) and 1,412 cases of single cancer which were matched for sex, age, year of diagnosis and site of cancer using the data of the Aichi Cancer Registry from 1962 to 1983. As to the family history of cancer three characteristics of multiple primary cancer were revealed, a larger percentage of cancer history in two or more members of their family (8.3% vs 3.6%), a larger percentage of a cancer history in sisters (11.2% vs 5.2%), and a larger percentage of family history of colorectal cancer (4.4% vs 1.6%). These differences were statistically significant and more pronounced in females. In male heavy smokers (30 or more cigarettes per day) the relative risk was elevated to 2.17, in particular for multiple primary cancers including lung cancer. In females the relative risk for drinkers and daily drinkers was 2.02 and 4.22 respectively. As to the kind of alcoholic beverage, the relative risk was highest for beer drinkers. Some kinds of occupations were related to increased or decreased risk of multiple primary cancers, especially in males. The data on family history suggest both genetic predisposition and environmental similarity among family members. Smoking, especially heavy smoking, could be a risk factor of multiple primary cancers which involve smoking-related cancers, but drinking seems to influence the multiplicity of cancer either directly or indirectly.