Unilateral Multicentric Breast Carcinoma Studied by Whole Mammary Gland Serial Sectioning.

The incidence and clinicopathologic features of unilateral multicentric breast cancer (UMBC)were studied by mammary gland serial sectioning in 116 cases of clinically defined monocentric breast cancer (MONBC) examined histopathologically at the Nagano Cancer Detection Center. UMBC was defined as: 1) histopathologically discontinuous tumors each with an intraductal spread, 2)at least one tumor-free section separating two tumors, and 3) a large primary tumor and other small secondary tumors. UMBC was detected in 23 of 116 cases (19.8%), all with one secondary tumor. Primary and secondary tumors were located in the same quadrant in 34.8% and in different ones in 65.2%. The secondary tumors were < 5 mm in size in 56.5%. Secondary tumors, averaging 8.3 mm in size and 25.5 mm in distance from the primary tumor, were almost exlcusively noninvasive carcinomas, including 15 (65.4%) noninvasive ductal carcinomas and several special types. The primary and secondary tumors were of the same histologic type in 3 of 23 cases. UMBC patients averaged 6 years younger than MONBC patients, and the incidence of UMBC tended to be higher in younger patients (P<0.1). UMBC tended to occur more frequently in quadrant B with an average histologic tumor size significantly smaller than that in MONBC (P <0.01). The histologic types of the primary tumor in UMBC and MONBC were similar, with common types predominant. Lymph node metastases tended to be slightly more frequent in MONBC. This high incidence of UMBC calls for careful attention when considering breast conserving therapy.