Primary small cell carcinoma of the lung initially presenting as a breast mass: a fine-needle aspiration diagnosis.

The incidence of metastases to the breast from extramammary sites is relatively low compared with the incidence of primary breast carcinoma. Primary sites which have a predilection for metastases to the breast include, in the order of decreasing frequency, malignant melanoma, lymphoma, lung carcinoma, ovarian carcinoma, and soft tissue sarcoma, followed by gastrointestinal and genitourinary primaries. Most lung primaries metastasizing to breast represent adenocarcinoma. Other types of lung carcinoma, including small cell carcinoma, are relatively rare. We report a case of lung small cell carcinoma metastasizing to the breast and initially presenting with a breast mass in a 50-year-old female. The tumor was first diagnosed on a fine-needle aspiration biopsy specimen (FNAB) from the breast lesion and subsequently supported by core biopsy. A discussion of the differential diagnoses to consider on FNAB follows. Because of the difference in treatment for primary small cell carcinoma of breast versus primary small cell carcinoma of the lung, as well as the difference in prognosis for both malignancies, determining the site of primary malignancy is crucial to adequate patient care.