Breast cancer multicentricity.

The reported incidence of breast cancer multicentricity has varied depending on the methods selected for sampling the apparently uninvolved portion of the breast, the distance a second cancer must be from the first cancer in order for it to be considered multicentric, and whether or not in situ carcinomas are included in calculations of multicentricity. In addition, the incidence of multicentricity may depend to some extent on the pathological stage and other histological characteristics of the primary index cancer. Bearing these various considerations in mind, one may estimate the overall rate of breast cancer multicentricity to be in the range of 25-50%. It also would appear that at least 5-10% of these multicentric cancers are invasive. Multicentric cancers do not appear limited to the breast quadrant that contains the primary index tumor, and they frequently involve breast tissue immediately subjacent to the nipple. In view of this incidence of multicentricity, if a breast cancer is treated by tylectomy one may predict that there will be a significant number of recurrences in the ipsilateral breast, although considerable time may be required before these additional breast cancers become clinically apparent. Whether or not recurrences of this type will increase breast cancer mortality is not known. Available data suggests that appropriate radiation to the apparently uninvolved portion of the breast may significantly reduce the chance of relatively short term recurrence. The effect of combining breast irradiation or adjuvant chemotherapy with tylectomy on long term survival is not known.