Bilateral cancer of the breast: a review of clinical, histologic, and immunohistologic characteristics.

The clinical, histologic, and immunohistologic characteristics of 19 synchronous and 47 metachronous bilateral breast cancers was compared. Patients with metachronous tumors were 5 years younger and more likely to have a family history of breast cancer than those patients with synchronous cancers. The nondominant synchronous cancer was usually discovered mammographically accounting for small, node-negative tumors, and high prevalence of in situ lesions. The same was true of the second metachronous tumor when discovered mammographically. Patients with metachronous cancers who were not in a follow-up program had second cancers with characteristics similar to incidentally diagnosed unilateral cancer. The mean interval between metachronous cancers was 101 months. Significantly more first metachronous tumors were invasive lobular cancers. Histologic type of the first and second tumor was the same in only 68% of synchronous and 61% of metachronous cancers. Combined histologic evidence and differentiation was concordant in only 13% and 22% of tumors, respectively. Immunoperoxidase studies were performed with two human milk fat globule antibodies. Each antibody reacted similarly in the first and second tumor in less than 50% of tumors and concordance was less than 25% when both antibody reactions were assessed. Differences in histologic evidence, differentiation, and immunohistologic reaction suggest that both synchronous and metachronous cancers are morphologically and functionally dissimilar.