Duodenal Metastasis in Triple-Negative Invasive Ductal Breast Carcinoma With Negative Mammography: A Case Report and Review of the Literature.

Breast cancer metastasis to the gastrointestinal tract is uncommon, and duodenal involvement is exceptionally rare. Those cases that do metastasize are reported to be lobular, with ductal carcinomas comprising only a small percentage of reported cases. Furthermore, these invasive carcinomas are typically estrogen receptor-, progesterone receptor-positive ± human epidermal growth factor receptor 2 malignancies. We present a unique case of a patient with duodenal metastasis as the first sign of metastatic breast cancer. The rarity of this case is highlighted by the fact that the patient had no known breast malignancy, and pathological findings revealed triple-negative invasive ductal carcinoma consistent with primary breast cancer. Diagnostic mammogram and ultrasound were negative for any lesions.