Breast Metastasis from Primary Lung Adenocarcinoma: A Rare Occurrence with Diagnostic Challenges and Treatment Implications.

Breast metastasis from non-mammary sites is a rare occurrence with a prevalence ranging from 0.5 to 3%. Accurate diagnosis is crucial as it influences treatment planning and management. Distinguishing primary breast cancer from metastatic disease can be challenging and an incorrect diagnosis can result in unnecessary surgical interventions. Immunohistochemistry plays a crucial role in identifying the primary tumour origin, especially when cytologic patterns appear atypical. Here, we present a case of a 53-year-old female patient with breast metastases from a primary lung adenocarcinoma. Pathology from the lung biopsy revealed a well to moderately differentiated adenocarcinoma with EGFR mutation. Immunohistochemical analysis using specific markers, such as TTF-1 and GATA-3, was instrumental in determining the malignant cell origin and formulating a treatment plan. This report highlights the importance of early diagnosis, thorough investigation, and the role of immunehistochemical markers in managing this rare occurrence.
Keywords: Breast metastasis, Lung cancer, Core biopsy, EGFR-mutation