RESUMEN
We report a rare case of pleomorphic carcinoma of the breast, suspected of being a granulocyte-colony stimulating factor (G-CSF)producing tumor, in a 75-year-old woman. She presented with a red and swollen breast, 3 weeks after undergoing core needle biopsy(CNB). Her leukocyte counts and C-reactive protein(CRP)levels were markedly high. At first, she was suspected to have an abscess and was initiated on a course of antibiotics. However, her condition rapidly deteriorated; therefore, she underwent an emergency mastectomy. Despite undergoing postoperative radiation therapy, 2 months after the operation, multiple metastatic foci were found in the lungs and liver, and she died of the disease 3 months after her first visit. After the operation, her leukocyte count had quickly returned to normal, but it increased as the disease progressed. These findings support the conclusion that this carcinoma was producing G-CSF. The final pathological diagnosis was G-CSF producing pleomorphic carcinoma of the breast.