Nab-paclitaxel (Abraxane for Injectable Suspension), at a dose of 150 mg/m2 weekly, improves overall survival (OS) to a much greater degree than conventional taxane monotherapy in women with previously untreated metastatic breast cancer (MBC), according to results of a phase II study released at the 34th Annual San Antonio Breast Cancer symposium (SABCS).

Nab-paclitaxel is a unique albumin formulation of a non-crystalline, amorphous form of paclitaxel in an insoluble nanoparticle state.

William Gradishar, MD, with Northwestern University Feinberg School of Medicine in Chicago, and colleagues presented results in 300 women with previously untreated MBC who were randomized to one of four treatment regimens. Treatments included nab-paclitaxel 300 mg/m2 every 3 weeks, 100 mg/m2 weekly for the first 3 of 4 weeks, 150 mg/m2 weekly for the first 3 of 4 weeks, or docetaxel 100 mg/m2 every 3 weeks.

Taxanes are considered standard treatment for MBC and are often used as adjuvant chemotherapy for patients with early-stage disease, Dr. Gradishar, professor of hematology/oncology, pointed out. Given that the best 5-year relative survival rate to date with taxanes is only 20% with a median survival of 2 to 3 years, there is an urgent need for agents with improved antitumor activity.

Patients enrolled in the present study were ≥ 18 years with stage IV pathologically confirmed adenocarcinoma of the breast, measurable disease, Eastern Cooperative Oncology Group performance status of 0 to 2, and no prior chemotherapy for MBC.

Results showed that nab-paclitaxel 150 mg/m2 weekly dose produced the longest OS. In fact, the median OS with the 150 mg/m2 weekly dose was 33.8 months, which represents a survival gain of 11.6 months over the 22.2-month median OS seen with the 100 mg/m2 weekly dose.

The median OS was 27.7 months in patients with nab-paclitaxel 300 mg/m2 every 3 weeks and 26.6 months with docetaxel 100 mg/m2 every 3 weeks.

Also, PFS was 10.9 months in patients on nab-paclitaxel 300 mg/m2 every 3 weeks, 7.5 months in patients on 100 mg/m2 weekly, 14.6 months in patients on 150 mg/m2 weekly, and 7.8 months in patients on docetaxel 100 mg/m2 every 3 weeks.

Within the 150 mg/m2 weekly treatment arm, the best response occurred at cycle 2, whereas dose reductions secondary to toxicities occurred at later treatment cycles.

Dr. Gradishar said that the data indicate that a 150 mg/m2 dose weekly may help patients achieve a clinical response before the onset of dose-limiting adverse events.

He speculated that nab-paclitaxel’s superior efficacy may be related its delivery of the albumin-bound cytotoxic drug preferentially to tumors secreting the SPARC protein.

Written by Jill Stein
Jill Stein is a Paris-based freelance medical writer.