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Nab-Paclitaxel Boosts Progression-Free Survival in Metastatic Breast Cancer

By Jill Stein

CHICAGO -- May 28, 2009 -- Nab-paclitaxel (Abraxane for Injectable Suspension) significantly lengthens the median progression-free survival (PFS) compared with docetaxel (Taxotere) in women with previously untreated metastatic breast cancer (MBC) and is also better tolerated, according to the findings of a phase 2 trial published online on May 26th in the Journal of Clinical Oncology.

The multicentre study found that nab-paclitaxel extended PFS by almost 7 months compared with the taxane docetaxel when the data were assessed by the study investigators and by more than 5 months when the data were assessed by independent radiologists.

The overall response rate (ORR), the primary endpoint, was higher with both weekly nab-paclitaxel regimens than docetaxel but was only significant by investigator assessment.

The results of the present study, if replicated in a phase 3 trial, "represent a key advance in the armamentarium of treatment for patients with MBC in the first-line setting," said William J. Gradishar, MD, Robert H. Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois.

In the multicenter trial, 302 women were randomised to treatment with nab-paclitaxel 300 mg/m² every 3 weeks, 100 mg/m² weekly, 150 mg/m² weekly, or docetaxel 100 mg/m² every 3 weeks.

Both 150 mg/m² and 100 mg/m² weekly nab-paclitaxel showed a higher ORR than docetaxel (49%, 45%, and 35% for the 3 groups, respectively) when assessed by independent radiologists, however the results were not significant, P = .224.

With investigator assessment, the differences between the weekly nab-paclitaxel doses and docetaxel reached statistical significance (P < .001).

Dr. Gradishar said that the lower ORRs recorded by independent radiological assessment is "common to this and other trials and may be explained in part by the fact that radiologists evaluate only imaging studies and not measurable, palpable disease such as skin nodules and peripheral lymph nodes."

Patients treated with nab-paclitaxel 150 mg/m² weekly had significantly longer PFS than docetaxel-treated patients when assessed by both the independent radiologists (12.9 versus 7.5 months, respectively, P = .0065) and the investigators (14.6 months versus 7.8 months, respectively, P = .012)

Review by both the investigator and the independent radiologists found a significantly higher disease control rate (DCR) in patients receiving either dose of weekly nab-paclitaxel compared with docetaxel.

The incidence of grade 3/4 fatigue, neutropenia, and febrile neutropenia was lower in all nab-paclitaxel arms than in the docetaxel arm while the incidence of peripheral neuropathy was similar in all treatment groups. The recovery from peripheral neuropathy appeared faster with all doses of nab-paclitaxel compared with docetaxel.

Dr. Gradishar added that nab-paclitaxel's better efficacy and tolerability may be due, in part, to its delivery of the albumin-bound cytotoxic drug preferentially to tumours secreting the SPARC protein, he added. Additional studies are needed to confirm this hypothesis.

Funding for the study was provided by Abraxis BioScience, Inc.

SOURCE: Journal of Clinical Oncology

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