Mitomycin C (MMC) is rarely used in first-line chemotherapy for advanced breast cancer, although the drug is reported to be active. Treatment with MMC is usually reserved for second- or third-line treatment. We have given MMC as second- or third-line treatment to 59 patients. Fifty-six patients were evaluable for response. No complete and only 3 partial responses were observed for an overall response rate of 5%. The median time to progression was 2 months and median survival time was 6 months. In this retrospective study MMC is demonstrated to be inactive in third-line chemotherapy.