Breast metastases from non-primary breast malignancies: What should we know?

Background: Metastases from extramammary malignant neoplasms are very rare, accounting for less than 2% of all breast malignancies.

Objective: The aim of this study is to describe the clinicopathological features and prognosis of breast metastases from non-primary breast malignancies at our institution.

Methods: We performed a retrospective observational study, obtaining data from electronic medical records and pathology databases between January 1985 and December 2020 for patients diagnosed with breast metastasis from non-primary breast malignancies. Only patients diagnosed by biopsy were included.

Results: Fifteen patients diagnosed with breast metastases from non-primary breast malignancies were included, 13 women (86,67%) and 2 men (13,33%). The median age at time of initial diagnosis was 56 years (IQR 21-68). The most frequent primary malignancy was melanoma (9/15; 60%). The median time to diagnosis of breast metastases was 65 months (IQR 13-106). The most common diagnostic modality was CT-scan (10/15; 66,67%). The median follow-up was 96 months (IQR 29-136). Eight patients underwent surgery (53,3%), being the most common surgical intervention breast-conserving surgery (5/8; 62,5%). Mortality at the end of follow-up was 53,3% (8/15). On the survival analysis, we found no differences between patients undergoing surgery and those only receiving systemic treatment [41,5 months (IQR 17,5-57,5) versus 14 months (IQR 2-24), respectively; p = 0,161].

Conclusions: Breast metastases from non-primary breast malignancies are extremely rare and represent a diagnostic and therapeutic challenge, due to the poor prognosis of these patients. Thus, arriving at the correct diagnosis is crucial to avoid unnecessary treatment in this population.