LAUSR

BACKGROUND The incidence of colon cancer is increasing worldwide. Treatments for colon cancer include surgery and surgery combined with chemotherapy and radiotherapy, but the median survival rate is still poor. Colon cancer most commonly metastasizes to the lymph nodes, lungs, liver, peritoneum, and brain, but breast metastasis is rare. There is no agreement on its treatment. CASE SUMMARY A 23-year-old woman was admitted to our hospital for further treatment with a history of acute abdominal pain, nausea, and vomiting. Her physical examination and computed tomography scan revealed an abdominal tumor. Transverse colectomy was successfully performed. Histopathological examination revealed that the tumor was a mucosecretory adenocarcinoma with signet ring cells. The patient inadvertently found a mass in the outer upper quadrant of the right breast after four cycles of XELOX chemotherapy [oxaliplatin 130 mg/m2, d1, intravenous (iv) drip for 2 h; capecitabine 1000 mg/m2, po, bid, d1–d14]. After discussion with the patient, we performed a lumpectomy and frozen biopsy. The latter revealed that the breast tumor was intestinal metastasis. Genetic testing showed wild-type RAS and BRAF. So we replaced the original chemotherapy with FOLFIRI [irinotecan 180 mg/m2, d1, iv drip for 3–90 min; leucovorin 400 mg/m2, d1, iv drip for 2 h; 5-fluorouracil (5-FU) 400 mg/m2, d1 and 5-FU 1200 mg/(m2 d) × 2 d, continuous iv drip for 46–48 h] + cetuximab (500 mg/m2, d1, iv drip for 2 h). Serum levels of tumor markers returned to normal after several treatment cycles, and there was no evidence of tumor recurrence or metastasis. CONCLUSION Breast metastasis from colon cancer is rare. Radical breast surgery should be avoided unless needed for palliation. Chemotherapy combined with targeted therapy should be the first choice.