Non-primary breast malignancies: a single institution's experience of a diagnostic challenge with important therapeutic consequences-a retrospective study.

Background: Breast cancer is a common malignancy, but metastases to the breast of extramammary malignancies are very rare. Treatment and prognosis are different. The aim of the study is to report the incidence of lymphomas and metastases to the breast of extramammary malignancies in our 30-year archive.

Methods: The pathology database of a single institute was reviewed for all breast neoplasms which were coded in our system as a metastasis in the period 1985-2014. Metastatic tumors from primary breast carcinoma were excluded.

Results: A total of 47 patients were included (7 men/40 women, mean age 63 years). The majority originated from lymphoma (n = 18) and primary melanoma (n = 11). Other primary tumor sites included the ovary (n = 6), lung (n = 6), colon (n = 3), kidney (n = 1), stomach (n = 1), and chorion (n = 1). In 24/47 patients (51 %), metastasis was the first sign of the specific malignant disease. In seven patients (15 %) surgery was performed, the diagnosis of metastatic disease was adjusted in four patients (9 %) postoperatively.

Conclusions: It is important to distinguish lymphomas and metastases to the breast from common primary breast carcinoma for proper treatment and prognosis. Therefore, we emphasize the need for a histological or cytopathological diagnosis before any treatment is commenced. The pathologist plays a key role in considering the diagnosis of metastasis if the histological features are unusual for a primary breast carcinoma. The pathologist should therefore be properly informed by the clinical physician although lymphomas and metastases to the breast are the first presentation of malignant disease in half the cases.