Abstract
INTRODUCTION: Breast metastases from primary colorectal carcinoma are extremely rare, with only 45 cases being reported previously. Since the most common malignancy in the breast and axilla is primary breast cancer regardless of cancer history, non-hematologic metastases may be misdiagnosed initially. Nevertheless, differentiating breast metastases from primary breast cancer is crucial because of their differences in prognosis and management. PATIENT CONCERNS: We present a case of a 44-year-old Asian woman who noticed a new right breast lump after undergoing surgery and chemotherapy for her primary sigmoid colon cancer. DIAGNOSIS: Image and immunohistochemistry findings were consistent with breast metastasis from primary colorectal adenocarcinoma. INTERVENTIONS: The patient underwent breast tumor excision and reinitiated chemotherapy. OUTCOMES: The patient's disease progressed despite the interventions. She passed away 7 months after the detection of breast metastasis. CONCLUSION: When a new breast lesion is detected in patients with colorectal cancer history, the physician should consider the possibility of breast metastasis due to the poor prognosis. If a biopsy is necessary, cancer history should be provided to the clinicians to prevent incorrect pathological interpretation. In establishing the diagnosis, certain immunohistochemical markers have been shown to be sensitive and specific in previously reported cases. The combination of tumor excision and chemotherapy was the most common strategy in managing this condition with inconsistent clinical outcomes.