The potential for carcinoma existing synchronously on a microscopic level within the second breast.

: In the present study, 23 of 314 patients presented with asymptomatic lesions in the second breast, comparing favorably with the incidence of asymptomatic carcinomas of the second breast reported in other series. The type of biopys used appears important, most surgeons advocating resection of a segment of breast ranging from 20 to 30 per cent of the quadrant being sampled. It appears that treatment of carcinoma of the second breast is essentially curative when the lesion is not noted clinically. Adequate treatment of the second breast lesion appears to reduce the at risk group within the second breast. It is usually stated that 10 per cent of patients will have a second carcinoma of the breast develop. In this study, metachronous lesions developed in six of 291 patients. Considering that these tumors all recurred in the outer quadrant of the remaining breast, the possibility arises that it may be more productive to do all biopsies in the tail of the second breast rather than to perform the so-called mirror image biopsy that was used in the present study. Results from this and other studies do appear to indicate that the utilization of a mirror image biopsy or outer quadrant biopsy is an effective way to detect and treat occult malignant tumors as well as the earliest forms of premalignant disease.