The influence of family history of cancer, irradiation and anticancer medication (mitomycin C), on the occurrence of multiple primary neoplasms with breast cancer--statistical analysis by the person-year method.

The influence of family history of cancer, radiation therapy and anticancer drug therapy (mitomycin C) on the occurrence of multiple primary neoplasms, following treatment of a first primary cancer of the breast, was analyzed by the person-year method in 1,359 patients, in Japan. During 14,371.8 person-years of observation, 111 multiple primary neoplasms including bilateral breast cancers were found in 109 patients. The incidence rate of multiple primary neoplasms were 0.00772 per person-year. The incidence in patients with a family history of cancer was 1.29 times greater than that in patients without such a family history, and the incidence in patients with a family history of breast cancer was about three times greater than that in those without it (p less than 0.01). Radiation therapy raised the occurrence of subsequent primary neoplasms 1.28-fold (or 1.62 fold after 5 years), and mitomycin C (a total dose of 0.8 mg/kg) therapy caused no increase in the occurrence of subsequent primary cancers, after an observation of 10 years or so.