Secondary colon malignancy is rare and has a nonspecific presentation. Breast cancer is the second most common malignancy that metastasizes to the gastrointestinal (GI) tract. Here, we present the case of a 54-year-old woman diagnosed with breast cancer and synchronous colon metastasis through a positive result obtained from stool occult blood screening. Colonoscopy revealed a subepithelial tumor of the colon. Biopsy revealed metastatic cancer with positive cytokeratin and GATA-binding protein 3 staining, as well as negative caudal-Type homeobox 2 staining. A palpable right breast mass with nipple retraction was found, and invasive lobular carcinoma (ILC) was diagnosed. Multiple bone, left adrenal gland, para-Aortic lymph node, and contralateral breast metastases were detected. Multimodality treatment involving systemic chemotherapy, hormone therapy, and modified radical mastectomy was applied. In our clinical experience, colon metastasis from breast cancer is rare and usually mimics primary colon cancer. High-Alert speculation and aggressive biopsy for patients with abnormal GI bleeding are indicated for diagnosis. Patients with colon metastasis from ILC of the breast have a poor prognosis. Therefore, multimodality treatments should be applied to improve their prognosis.
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