Breast and Axillary Metastases from High-grade Serous Ovarian Carcinoma: A Rare Case Report Highlighting Diagnostic Challenges and Pitfalls

High-grade Serous Ovarian Carcinoma (HGSOC) is an aggressive malignancy that commonly metastasizes to peritoneum, omentum, pelvic and para-aortic lymph nodes, serosal surfaces of bowel and mesentery. Metastases to the breast and axillary lymph nodes is extremely rare and can closely mimic primary breast malignancy, making diagnosis extremely difficult, especially if it occurs after a prolonged disease-free interval. A 35-year-old nulligravid woman presented with a painless right breast lump of two months’ duration along with bilateral axillary lymphadenopathy. She had already been diagnosed with HGSOC six years prior, for which she received neoadjuvant chemotherapy, optimum cytoreductive surgery, and several lines of chemotherapy. On radiological assessment, a suspicious right breast lesion with bilateral axillary lymph node enlargement and pleural effusion was discovered during the current presentation. Core biopsies from the right breast lesion and axillary lymph nodes showed a highgrade malignant epithelial tumour arranged in papillary pattern. Metastatic HGSOC was confirmed by immunohistochemistry, which showed positive expression for PAX8, WT1, CK7 with aberrant p53 and negative for breast-specific immunohistochemistry markers ER, PR, HER2, and GATA3. Given the chemoresistant disease and symptomatic breast lesion, the patient was treated with palliative local radiation, after which she experienced symptomatic relief and stable disease at short-term follow-up. The case highlights the importance of careful histopathological examination supported by an appropriate immunohistochemistry panel in making the correct diagnoses at unusual metastatic sites with long latency periods which can cause diagnostic confusion with primary breast carcinoma and prompted this case presentation.