We designed and implemented a new mitoxantrone-based high-dose chemotherapy regimen to minimize pulmonary injury (seen in carmustine-based regimens) in patients with breast cancer. One hundred and ninety-one breast cancer patients (99 stage II/IIIA; 27 stage IIIB; 65 stage IV responsive to conventional-dose chemotherapy) were treated with high-dose chemotherapy (CTM) delivered over 4 days (cyclophosphamide (6 g/m2), thiotepa (600 mg/m2), and mitoxantrone (24-60 mg/m2)) followed by autologous hematopoietic stem cell rescue. Stage II/III patients received chest wall radiation and tamoxifen (if hormone-receptor positive) after CTM. The 5-year event-free survival (EFS) for stage II/IIIA patients with 10 or more involved axillary lymph nodes (n = 80) was 62 +/- 12%. Hormone receptor-positive patients with 10 or more nodes did significantly better than negative patients. The EFS for stage IIIB patients at 5 years was 44 +/- 19%; for stage IV patients at 5 years was 17 +/- 10%. Stage IV patients achieving complete response in viscera and/or soft tissue prior to CTM did significantly better than those achieving a partial response. There were six (3%) treatment-related deaths including two due to diffuse alveolar hemorrhage. There were no episodes of delayed interstitial pneumonitis. There were six severe cardiac events in 91 patients (6.6%) but none after instituting mitoxantrone dose-adjustment in the final 100 patients. We conclude that CTM is associated with a low treatment-related mortality and little pulmonary toxicity. CTM produces excellent outcomes in stage II/IIIA patients with 10 or more involved axillary lymph nodes.