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

Aims: To review and illustrate the findings in fine needle biopsy (FNB) of extramammary malignancies presenting with breast metastases (MMB).

Methods: We reviewed 32 cases of MMB diagnosed on breast FNB. The clinical data, with particular attention to the history of a known primary malignancy, previous systemic metastatic disease in other sites and presentation with extramammary disease in addition to a breast mass were examined. The morphological appearances were reviewed and are illustrated, focusing on those features which allow the pathologist to recognise the possibility of metastatic disease and undertake appropriate steps to investigate this.

Results: The 32 cases included metastases from a wide range of sites, including cutaneous melanoma (10), lung (8), non-Hodgkin's lymphoma (5), soft tissue (4), colon (2), endometrium, ovary and bladder. There was a history of extramammary malignancy in 26, while in six patients the breast mass was detected at initial presentation with malignant disease. Of the latter six patients, four had evidence of widespread metastases, while one presented with multiple breast masses. In 16 cases the cytological features allowed the possibility of metastases to be recognised without clinical data, while in the other 16 there was sufficient overlap with primary mammary carcinoma that the possibility of metastases could be missed. Only one case was initially mistaken for a primary tumour, in this case the history of prior malignancy with systemic metastases was not provided to the reporting pathologist.

Conclusion: 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.