Based on the recommended phase II doses for doxorubicin (60 mg/m2) and docetaxel (60 mg/m2) and the National Surgical Adjuvant Breast and Bowel Project's (NSABP) experience with doxorubicin and cyclophosphamide (cyclophosphamide 600 mg/m2), we conducted a phase II trial at 18 institutions using doxorubicin/docetaxel/cyclophosphamide (ATC) given every 21 days, in preparation for a major adjuvant breast cancer study (NSABP B-30), in which ATC would be used. Eligibility requirements included measurable stage IIIB/IV breast cancer, performance status 0-2, normal left ventricular ejection fraction, and no prior chemotherapy for metastatic disease (nontaxane adjuvant chemotherapy was allowed if completed > 12 months before entry and if the cumulative dose of doxorubicin was =240 mg/m2). Eighty-nine patients were entered who ranged in age from 30-78 years (38.2% < 50 years; 61.8% =50 years). A total of 33.7% of patients had stage IIIB disease, and 66.3% had stage IV disease. Among the stage IV patients, 20.3% had received prior adjuvant chemotherapy. Dexamethasone premedication (8 mg p.o. b.i.d. for 3 days) and prophylactic ciprofloxacin (500 mg p.o. b.i.d. days 5-15) were used. Colony-stimulating growth factors were reserved for secondary prophylaxis after prolonged or febrile neutropenia (FN) or documented severe infection in a prior cycle. After a cumulative dose of doxorubicin 480 mg/m2, patients could continue with docetaxel/cyclophosphamide alone. Eighty-nine patients and 577 courses were evaluable for toxicity. Median time on study as of May 2002 was 36.5 months (range, 28-47 months). Febrile neutropenia occurred in 34 patients (38%); 8 developed FN in the absence of prior prophylactic growth factor support; 26 developed FN despite prior growth factor support (for one patient this information was unavailable). There were no septic deaths. One patient died from pulmonary embolism. Other grade 3/4 adverse events included: nausea (9%), vomiting (7%), stomatitis (6%), diarrhea (4%), arthralgia/myalgia (3%), and neurotoxicity (1%). Clinical congestive heart failure was seen in 3 patients (3.4%). Seventy-seven patients were evaluable for best response within 6 cycles of therapy. Thirteen patients (16.9%) had a complete response, 43 (55.8%) had a partial response, for an overall response rate of 72.7%. The median response duration was 23.8 months (95% CI, 16.2-37.8 months), and the median time to progression or death was 23.5 months (95% CI, 16.3-38.7 months). The median survival time was 35.6 months (95% CI, 26.6-39.4 months). The administration of ATC with primary ciprofloxacin and secondary colony-stimulating factor prophylaxis is feasible and active. Its value in the adjuvant setting is currently under investigation.