The significance of malignancies incidental to microcalcifications in breast spot localization biopsy specimens

Background: Incidental breast cancer is occasionally found in spot localization biopsy specimens adjacent to mirocalcifications in benign breast disease. Because this phenomenon could prove problematic for percutaneous sampling of microcalcifications without excisional biopsy, we studied surgical specimens from patients with cancers incidental to microcalcifications and compared them with specimens with microcalcifications within the malignancy. Methods: The pathology database at the Mount Sinai Medical Center from January 1993 to July 1998 was reviewed to identify breast cancer patients who underwent spot localization biopsy for microcalcifications. Patients presenting with microcalcifications within malignancy (determinate) were compared with patients with mirocalcifications in benign breast tissue adjacent to malignancy (incidental). Results: Thirty-two (13%) of the 241 specimens had microcalcifications in benign tissue adjacent to malignancy and 209 (87%) had microcalcifications within the malignancy. Fifty-six percent of the incidental cases and 65% of the controls had ductal carcinoma in situ. Infiltrating lobular carcinoma accounted for 25% of the incidental cancers and 2% of the determinate cancers (P <0.001). Fifty-seven percent of the infiltrating carcinomas incidental to mammographic findings were infiltrating lobular carcinoma compared with 7% of the nonincidental infiltrating carcinomas. None of the incidental invasive carcinomas were poorly differentiated (P = 0.002). There were no significant differences with regard to age, tumor size, stage, differentiation, estrogen and progesterone receptors, type of surgery and final margin status. In none of the patients with incidental malignancies did local or distant recurrences develop. Conclusions: Incidental carcinomas were found in 13% of spot localization biopsy specimens obtained for suspicious mammographic microcalcifications and have a favorable prognosis. Infiltrating lobular carcinomas are more commonly found with incidental microcalcifications than with determinate microcalcifications, and incidental invasive carcinomas are less likely to be poorly differentiated. The majority of malignancies, both determinate and incidental to microcalcifications, are due to ductal carcinoma in situ. Incidental malignancies commonly occur adjacent to fibrocystic changes and their other pathologic characteristics are not significantly different from nonincidental carcinomas. Despite the absence of radiographic findings, these patients can be successfully treated with breast conservation.