Tissue Microarray Study Suggests Paclitaxel Improves Outcomes for Women with Basal Type Breast Cancer

In the quest to improve personalization of cancer treatment, the CALGB (Cancer and Leukemia Group B) Cooperative in Canada discovered that women with basal type breast cancer benefit from adding paclitaxel (Taxol) to standard chemotherapy. Torsten O. Nielsen, MD, PhD, University of British Columbia, Vancouver, Canada, shared the group’s findings at the ASCO Breast Cancer Symposium in San Francisco, California.

He explained that the CALGB 9344 trial, which opened in 1993, involved more than 3100 women with breast cancer at high risk of relapse. The trial investigated adding a taxane to standard chemotherapy. Dr Nielsen said that, overall, the combination treatment was associated with “a statistically significant and clinically important 5% improvement in survival.”

At the time, data indicated that women whose tumors were HER2-negative and estrogen-receptor (ER)—positive saw no benefit from the combined treatment. Researchers used tissue microarray to help determine why some women derived greater benefit from paclitaxel. They used the new microassay method to examine preserved tissue samples from the breast tumors of 2039 patients who participated in the trial.

They stratified the tumors according to the 4 major molecular breast cancer subtypes: Luminal A, which is the most common, was identified in 790 specimens; ER-positive Luminal B comprised 340 tumors; HER2 types accounted for 221; and 444 were basal subtype tumors. Another 93 were ER-negative, HER2-negative, nonbasal tumors.

Women with basal tumors who received paclitaxel were 25% less likely to experience relapse in the more than 10 years of follow up (HR, 0.75; P = .033). They also had a 10% improvement in survival. This is important, because basal-type breast cancer is “quite aggressive, especially over the first 3 to 5 years, with a high death rate,” Dr Nielsen said. “For this basal type, we don’t have a specific targeted therapy and it affects young women. It has a predilection for African American women, and we clearly need some improved options for these women.”

Those with HER2, another aggressive cancer, also benefited from paclitaxel, showing a 20% advantage in relapse-free survival compared with women who had Luminal A tumors. The patients with Luminal A and B subtypes, who represented more than half of the study population, derived no clinical benefit from treatment with paclitaxel. “It only brought the extra costs and toxicities,” Dr Nielsen said.

Dr Nielsen said tissue microarray and the identification of new molecular markers are important steps in helping to determine which treatments work best in which patients, particularly in large-scale clinical trials. Lori Pierce, MD, University of Michigan, Ann Arbor, who moderated the presentation, agreed. “This is a very important study because the methods used will help clinicians select those breast cancers that will respond to specific chemotherapies and then spare patients whose cancer will not respond to specific agents,” she said.

Although these data come from a retrospective analysis, the size of the study lends weight to the findings. This study is likely to have an impact on future treatment recommendations regarding taxanes in breast cancer. Abstract No. 23.