Carcinoid metastatic to breast diagnosed by fine-needle aspiration biopsy

We report a patient in whom fine-needle aspiration biopsy of a breast mass, clinically suspected to be a mammary adenocarcinoma, established the diagnosis of a carcinoid metastatic to breast. The aspirate smears resembled a primary breast carcinoma; however, subtle cytomorphologic differences were present. Ultrastructural and immunohistochemical studies of the aspirated material confirmed the diagnosis of metastatic carcinoid.