Epidemiology of minimal breast cancer.

A case-control study conducted within the Breast Cancer Detection Demonstration Project allowed comparison of epidemiologic factors for benign breast diseases (n = 1,404), in situ cancer (n = 199), small (less than or equal to 1 cm) invasive cancer (n = 210), and larger invasive cancer (n = 788). Control subjects consisted of program participants who were not recommended for breast biopsy. Relationships were similar for small and larger invasive tumors, both showing associations with family history of breast cancer, age at first live birth, history of bilateral oophorectomoy, and obesity. In situ cancer was affected by family history and age at first childbirth but not by oophorectomy or obesity. These findings support the notion that "minimal" breast cancer is indeed cancer. In addition, the results suggest that hormonal influences early in life may initiate the carcinogenic process, while those that operate later may enhance the progression from in situ to invasive disease.