Unmasking hidden metastasis: A case report of gastrointestinal metastasis detected a decade after breast cancer diagnosis.

Breast cancer is among the most common malignancies in women, and metastasis significantly impacts survival and quality of life. Although many patients remain disease-free in the early years after surgery and adjuvant therapy, occult metastasis remains a major clinical concern. While bone, lung, and liver are common metastatic sites, gastrointestinal involvement is rare and often overlooked. Recent evidence suggests that late-stage occult metastasis can develop even after long disease-free intervals. Early detection is vital for optimizing treatment and improving prognosis. Therefore, gastrointestinal symptoms such as abdominal pain, altered bowel habits, or unexplained weight loss in breast cancer patients warrant prompt imaging and endoscopic evaluation. This case report describes a 49-year-old woman with invasive lobular breast carcinoma who, after nearly 11 years of recurrence-free survival, presented with constipation and weight loss. Imaging and endoscopy revealed gastric and rectal metastases, underscoring the risk of occult metastasis in breast cancer. This case highlights the importance of considering age and treatment history when developing personalized management strategies and emphasizes early detection and intervention to improve outcomes and quality of life. Computed tomography revealed thickening of the gastric antrum and rectal wall, resulting in luminal narrowing. A comprehensive flexible colonoscopy was performed, and biopsy of the colonic tissue for pathological examination indicated metastatic tumors in the rectal mucosa originating from breast cancer as well as metastatic lobular carcinoma in the stomach. The patient is currently receiving a chemotherapy regimen of gemcitabine 1.4 g and carboplatin (500 mg). The patient is currently in the chemotherapy phase, and close monitoring of the condition is being conducted during treatment. For patients with a history of breast cancer, the emergence of new gastrointestinal symptoms or a diagnosis of primary gastric or colorectal cancer should raise suspicion metastatic breast cancer. During the biopsy process, a comprehensive evaluation of histopathological and immunohistochemical analyses is necessary, and these results should be compared with those of primary breast cancer to ensure an accurate diagnosis.