Non-Mammary Metastasis to Breast; a Diagnostic Challenge

Background: Non-mammary metastasis to the breast poses a diagnostic challenge for the pathologists especially when no prior history of non-mammary malignancy is provided. Since non-mammary metastasis is not a very common occurrence, there is a chance that it can be easily missed especially with overlapping morphology and unknown prior history of any malignancy. Methods: In total, ۴۰ patients matching our inclusion criteria were identified through hospital information system in a ۱۰-year period. Confirmatory stains were used to confirm the diagnosis. Results: The most common primary malignancy site was gastrointestinal tract comprising ۳۵% of the metastasis. This was followed by small cell carcinomas (۱۷.۵%). In addition, in ۷۲.۵% of the patients, there was a known history of primary malignancy but only in ۱۸ (۴۵%) of the cases, the clinicians mentioned it on the biopsy request form. For the remaining cases (۲۷.۵%), the clinician was contacted after the verification of the report and was asked to evaluate the possibility of metastasis from the known primary site. Conclusion: Identifying the non-mammary metastasis is important at the time of initial diagnosis as it can prevent the patient from extensive surgery, which might not be needed, if it is not a primary breast tumor. Provision of prior history and use of immunohistochemical stains can aid in timely and accurate diagnosis.