Update: the M.D. Anderson Cancer Center experience with paclitaxel in the management of breast carcinoma.

The first of three trials at M.D. Anderson Cancer Center investigating paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) in metastatic breast cancer was a phase II study involving 25 patients (297 courses) previously treated with only one chemotherapy regimen; the patients received paclitaxel 250 mg/m2 infused over 24 hours without granulocyte colony-stimulating factor (G-CSF). Complete (12%) and partial responses (44%) led to median durations of response and survival of 9 and 21 months, respectively. The median paclitaxel dose was 200 mg/m2. Despite profound neutropenia (median granulocyte count of 0.3 cells x 10(9)/L for the first three courses), infection occurred in 42% of patients but only 6% of courses. In a phase I trial of paclitaxel 125 mg/m2 over 24 hours followed by doxorubicin 60 mg/m2 using G-CSF at 5 micrograms/kg days 5 through 19, dose-limiting mucositis with neutropenic fever occurred at the starting dose, so the maximum tolerated dose was one dose lower: paclitaxel 125 mg/m2 (over 24 hours) followed by doxorubicin 48 mg/m2 over 48 hours. Among 10 patients, there was one complete response and seven partial responses (overall response, 80%). Suspecting a schedule-dependent interaction between drugs, a phase I trial of the reverse sequence yielded a maximum tolerated dose, defined by neutropenic fever without mucositis, of doxorubicin 60 mg/m2 (over 48 hours) followed by paclitaxel 150 mg/m2 (over 24 hours) in 21 patients. A pharmacokinetic study in which the sequence of administration of paclitaxel over 24 hours and doxorubicin over 48 hours was alternated in courses 1 and 2 indicated that when paclitaxel by 24-hour infusion is given first, doxorubicin plasma levels at the end of infusion were an average 70% higher and doxorubicin clearance was reduced approximately 30% compared with the reverse sequence. Similarly, the incidence of grade 2 or 3 mucositis was 70% with the paclitaxel/doxorubicin sequence versus only 10% with the reverse sequence. We concluded that paclitaxel slows doxorubicin metabolism and that when used together in this schedule, doxorubicin should precede paclitaxel. In the third trial paclitaxel without G-CSF was administered to two groups of heavily pretreated patients: (1) those with only two prior chemotherapy regimens (inclusive of adjuvant therapy) received paclitaxel 175 mg/m2 over 24 hours and (2) those with three or more prior regimens received paclitaxel 150 mg/m2 over 24 hours. Response rates in both regimens were approximately 20%. We conclude that paclitaxel has significant antitumor activity in metastatic breast cancer, especially in patients with limited prior therapy, without need for G-CSF.(ABSTRACT TRUNCATED AT 400 WORDS)