Non-Mammary Metastasis To Breast; A Diagnostic Challenge: Non-Mammary Metastasis to Breast

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, 40 patients matching our inclusion criteria were identified through hospital information system in a 10-year period. Confirmatory stains were used to confirm the diagnosis.Results: The most common primary malignancy site was gastrointestinal tract comprising 35% of the metastasis. This was followed by small cell carcinomas (17.5%). In addition, in 72.5% of the patients, there was a known history of primary malignancy but only in 18 (45%) of the cases, the clinicians mentioned it on the biopsy request form. For the remaining cases (27.5%), 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.