Synchronous and metachronous malignancies in patients with melanoma: a clinicopathologic study highlighting the role of fine-needle biopsy cytology and potential diagnostic pitfalls.

Fine-needle biopsy (FNB) is commonly used in the investigation of patients with a history of melanoma who present with possible metastatic disease. Non-melanoma malignancies (NMM) are common in the general population and not infrequent in patients with melanoma. Such tumors may be difficult to distinguish from metastatic melanoma on FNB. We sought to determine the types of NMMs that occur in melanoma patients, to document the frequency with which they were diagnosed by FNB, and to highlight potential pitfalls in cytologic diagnosis. NMMs occurring in 1416 consecutive melanoma patients who underwent FNB of 2204 clinically suspicious lesions between 1992 and 2002 at a single center were reviewed and analyzed. The sites of FNB included lymph nodes (36.9%), skin and subcutis (25.1%), visceral locations (17.9%), and other sites (20.0%). Of the 1416 melanoma patients investigated by FNB, 116 (8.2%) had a metachronous or synchronous NMM; the NMM was diagnosed by the FNB in 17 (14.7%) patients. The most common NMMs were epithelial tumors (69.4%, most commonly carcinomas of large bowel, breast and prostate) and hematologic malignancies (21.8%). As NMMs are not infrequent in patients with melanoma, they should always be considered in the differential diagnosis of clinically suspicious masses in patients with a history of melanoma, as well as in patients at high risk of melanoma. Careful assessment of the FNB cytologic features and directed use of ancillary studies should enable accurate diagnosis in most cases and facilitate appropriate patient management.