A case of occult breast cancer presenting with intestinal obstruction as the initial symptom.

Occult breast cancer (OBC) refers to a type of breast cancer where no primary lesion is detected through physical examination, imaging, and pathology. This report presents a clinical case of OBC with intestinal obstruction as the initial symptom. A 67-year-old female with no underlying conditions presented to Zhuzhou Hospital Affiliated to Xiangya School of Medicine, Central South University with intestinal obstruction. Contrast-enhanced CT of the abdomen showed thickening of the lower rectum and ascending colon, suggestive of a neoplastic lesion. Chest CT showed multiple enlarged lymph nodes in the left axilla. Colonoscopy revealed only mucosal congestion, roughness, and thickening. Suspecting an intestinal tumor, laparoscopic radical resection of the rectal stenosis was performed. Postoperative pathology indicated poorly differentiated adenocarcinoma of the rectum. Immunohistochemistry showed positive expression of estrogen receptor (ER), progesterone receptor (PR), GATA-binding protein 3 (GATA3), and cytokeratin 7 (CK7), suggesting breast cancer metastasis. Breast MRI revealed multiple proliferative nodules in both breasts (breast imaging reporting and data system, BI-RADS 2). Biopsies of the right lower-inner breast, bilateral axillary, and supraclavicular lymph nodes were performed. No carcinoma was found in the right breast tissues; however, small foci of carcinoma was detected in the right axillary lymph nodes, and poorly differentiated carcinoma of suspected breast origin was found in the bilateral supraclavicular and left axillary lymph nodes. The final diagnosis was OBC with lymph node and rectal metastasis. The patient died 16 months postoperatively. OBC often lacks identifiable primary breast lesions, and gastrointestinal metastases are particularly rare. Clinical manifestations are frequently masked by symptoms of metastatic lesions, making diagnosis challenging. Clinicians should maintain a high index of suspicion. Due to rapid disease progression and multiorgan involvement, prognosis is extremely poor. Early identification of the primary lesion in OBC is crucial for improving outcomes.