Synchronous and metachronous carcinoma of the breast.

To determine the incidence of synchronous bilateral breast cancer, 100 women receiving their initial treatment for primary breast cancer prospectively underwent biopsy of the opposite breast. No patient had a clinically detectable abnormality in the contralateral breast, but 2% had unsuspected invasive ductal carcinomas. An additional 5% had premalignant lesions. To determine the incidence of the development of metachronous breast cancer, 153 women who underwent surgical treatment of primary breast cancer between 1955 and 1979 were followed from 2 months to 26 years, with an average of 3.6 years. During that time, 3.9% developed metachronous carcinomas of the contralateral breast.