Clinicopathologic characteristics of 143 patients with synchronous bilateral invasive breast carcinomas treated in a single institution

BACKGROUND. Synchronous bilateral invasive breast carcinoma (SBIBC) ranged in incidence from 0.3% to as high as 12%. METHODS. Between April 1997 and February 2003, 143 consecutive patients with SBIBC were treated at the European Institute of Oncology (Milan, Italy). Their information was collected prospectively in a database. The bilateral tumors were divded into left and right tumors. Tumor size, histology, grade, lymph node status, estrogen (ER) and progesterone receptor (PgR) status, HER-2 expression, peritumoral vascular invasion (PVI), Ki-67 expression, extensive in situ component (EIC), and multifocality between the two groups were analyzed. During the same time period, 6218 patients with unilateral invasive breast carcinoma (UIBC) were analyzed in the same manner for comparison with the patients with SBIBC. RESULTS. There were no significant differences between left and right tumors, and the observed histopathologic agreement within the same patient was significantly superior than statistically expected for all characteristics except size, lymph node status, and multifocality. When compared with patients with UIBC, patients with SBIBC were more likely to present with smaller tumors and showed a higher frequency of invasive lobular carcinoma, lower histologic grade, higher rate of ER and PgR positivity, and lower PVI and Ki-67 expression. CONCLUSIONS. The high concordance of histopathologic characteristics between SBIBC within the same patient could reflect a particular hormonal environment that influenced either the initiation and development of these lesions simultaneously and independently from the single or multi-clonal origin, either a less aggressive biological behavior compared with UIBC. In particular, the strong agreement of the observed EIC in SBIBC within the same patient seemed to definitively exclude the metastatic origin of these tumors.