Diagnosis of extramammary malignancy metastatic to the breast by fine needle biopsy

The majority (81%) of cases of MMB have a history of primary malignancy, although only a minority have a history of systemic metastases at other sites. Of those patients without known prior malignancy, the majority present with systemic disease or multiple breast lesions. The cytological features allow metastatic disease to be suspected in half of the cases, although in the others, particularly patients with metastatic adenocarcinoma, diagnosis without recourse to immunohistochemistry is difficult or impossible. A combination of complete clinical history, attention to the cytological features and suspicion in cases with metastatic disease beyond the axilla should allow most cases of MMB to be suspected, and suitable material for ancillary confirmatory testing to be obtained.