Epidemiology of minimal breast cancer among women screened in New York City.

A case-control study based on a screened population in New York City examined epidemiologic risk factor differences between minimal breast cancer (in situ and small invasive carcinomas) and all other breast carcinomas, referred to as clinical breast cancer. Histopathologic re-review of the original slides identified 113 minimal and 792 clinical breast cancers among 1,290 eligible cases; 2,173 randomly selected screenees served as controls. Among those who developed cancer, black women were twice as likely to develop minimal, as compared to clinical, breast cancer. Women who were less than 20 years of age at first live birth had more than double the probability of being diagnosed with minimal breast cancer, whereas women with first live birth at age 30 years or greater and nulliparous women were at 1.5 times the risk of clinical breast cancer. The relative proportion of minimal breast cancer increased with increasing number of children breast fed, being twofold among women who nursed 2 children or more. Unlike clinical breast cancer, minimal breast cancer was not associated with either family history of breast cancer or obesity. Meaningful histologic differences were not apparent between the case subgroups. Except possibly for obesity, these results could not be explained by any plausible diagnostic bias.