Small intestinal metastasis of triple-negative breast cancer mimicking lymphoma: imaging findings and case report.

Small intestinal metastasis from breast cancer is a rare entity with non-specific clinical presentations, rendering it susceptible to missed or delayed diagnosis. Herein, we present a rare case of breast cancer metastasizing to the small bowel, with unexplained anemia as the sole initial clinical complaint.The patient manifested persistent dizziness and palpitations, accompanied by repeatedly positive fecal occult blood testing, and carried a well-documented history of surgical resection for bilateral breast malignancy.Contrast-enhanced computed tomography (CT) of the small bowel demonstrated segmental, asymmetric wall thickening with adjacent lymphadenopathy and no luminal stenosis; the thickened wall exhibited heterogeneous enhancement, raising initial suspicion of lymphoma. Subsequent double-balloon enteroscopy(DBE) identified a large circumferential deep ulcerative lesion, which was endoscopically indistinguishable from primary small bowel adenocarcinoma or intestinal lymphoma. The definitive diagnosis of small intestinal metastasis from breast cancer was established by histopathological and immunohistochemical evaluation, in conjunction with the patient's oncological history. A review of the literature indicates that small intestinal metastasis from breast cancer is more commonly associated with invasive lobular carcinoma, and affected patients usually present during routine surveillance or with abdominal pain. In the present case, the primary pathology was invasive ductal carcinoma of triple-negative phenotype (TNBC), and the patient's initial presentation with anaemia constitutes an atypical manifestation. Clinicians should maintain a high index of suspicion for small bowel metastasis in breast cancer survivors who develop unexplained anemia, positive fecal occult blood, or abnormal small intestinal imaging, even in the absence of classic gastrointestinal symptoms. A multidisciplinary approach integrating imaging, endoscopy, pathology, and immunohistochemistry is essential to minimise diagnostic delay and avoid misdiagnosis.