Breast metastases from nonmammary malignant neoplasms are uncommon, accounting for approximately 2% of breast tumors. There are 13 cases reported in the literature of carcinoid tumor metastatic to the breast, and more than half of these cases were misdiagnosed pathologically and treated as primary breast carcinoma, even in cases with a medical record of carcinoid tumor. We describe a patient with a history of asthma and diarrhea who presented to the University of Arkansas for Medical Sciences, Little Rock, with an exacerbation of the asthma. The results of routine physical examination revealed a mass in the left breast. A diagnosis of carcinoid tumor metastatic to the breast was made after a partial mastectomy was performed. The differential diagnosis between primary carcinoid tumor of the breast and carcinoid tumor metastatic to the breast is often controversial in surgical pathology. Diagnoses need to be made correlating clinical and histological examination in difficult cases in which there is not a diagnosis of carcinoid tumor elsewhere. Accurate diagnosis of breast metastases is important to avoid unnecessary treatment.
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