Small cell carcinoma of the breast.

Small cell carcinoma of the breast (SCCB) is an uncommon neoplasm that accounts for less than 1% of primary breast cancers. Histologically, these tumors have striking similarities to small call carcinoma of the lung, usually with evidence of associated ductal carcinoma-in-situ (DCIS) with areas of ductal, lobular, or papillary differentiation. Immunoreactivity for neuroendocrine markers is documented in two thirds of cases, while 33% to 50% are positive for estrogen receptor (ER) or progesterone receptor (PR). Her2/neu expression has not been reported in SCCB. Treatment, which may include surgery, radiotherapy, and combination chemotherapy, is based on clinical stage and the presence of metastases. Prognosis is variable and is dependent on the initial stage of disease.