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SWOG-S0226: Drug combo performed better in treating hormone-sensitive breast cancer
San Antonio Breast Cancer Symposium
SAN ANTONIO — Combination anastrozole and fulvestrant bested anastrozole alone in terms of PFS, as well as OS, in postmenopausal women with hormone receptor-positive breast cancer, a speaker said here.
In the SWOG-S0226, phase 3 clinical trial, Rita Mehta, MD, of the University of California, Irvine Medical Center, and colleagues randomly assigned 707 patients with metastatic hormone receptor-positive breast cancer to receive 1 mg anastrozole (Arimidex, AstraZeneca) daily or a combination of 1 mg anastrozole daily and fulvestrant (Faslodex, AstraZeneca) between 2004 and 2009. They administered fulvestrant intramuscularly, using a 500-mg loading dose on day 1 followed by 250 mg on days 14 and 28, and a 250-mg monthly maintenance dose thereafter. The researchers also strongly encouraged patients in the anastrozole-only arm to crossover to fulvestrant after disease progression.
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The researchers included 694 patients in the analysis. According to results, median PFS was 13.5 months in the anastrozole arm and 15 months in the combination arm (HR=0.8; 95% CI, 0.68-0.96), Mehta said during a presentation. Among the 60% of women who had not received prior adjuvant tamoxifen treatment, median PFS was 12.6 months in the anastrozole-only group compared with 17 months in the combination therapy group (HR=0.74; 95% CI, 0.59-0.92). In contrast, among the 40% of women pretreated with tamoxifen, median PFS was 14 months in the anastrozole arm vs. 15.5 months in the combination arm, with an HR of 0.89. The P value, however, did not reach statistical significance, Mehta said.
Results also suggested a trend toward improved median OS among all patients in the combination arm (47.7 months), as compared with the anastrozole-alone arm (41.3 months), with an HR of 0.81 (95% CI, 0.65-1). Further, in patients with no prior tamoxifen treatment, median OS was 39.7 months in the anastrozole-only group vs. 47.7 months in the combination therapy group (HR=0.74; 95% CI, 0.56-0.98). However, it is too early to determine whether prior tamoxifen treatment is a predictive factor, according to Mehta.
“We need to better understand other possible factors, since the prior tamoxifen factor could be a false lead from an unplanned analysis,” Mehta said.
In the combination arm, the researchers also found two deaths attributable to pulmonary embolism and one attributable to cerebrovascular ischemia. There was also one patient with grade-4 pulmonary embolism and one with grade-4 neutropenia and lymphopenia in this group. In the anastrozole-only arm, four patients experienced grade-4 toxicities, such as thrombosis/embolism, arthralgia, thrombocytopenia and dyspnea. Grade-3 toxicities were rare, Mehta said, with 13% occurring in the combination therapy group and 11% in the anastrozole-only group. These included musculoskeletal pain, fatigue, hot flashes, mood alterations and gastrointestinal symptoms with a frequency ranging from 1% to 4%. However, only four patients in the anastrazole arm and 11 in the combination arm discontinued treatment due to adverse events or side effects.
Regarding future directions for study, Mehta said, “The next step for researchers would be to try the combination in even earlier stages of breast cancer to test whether long-term cures could be increased at those stages.”
Disclosure: Dr. Mehta has received grant or research support from AstraZeneca.
Earn CME this spring at the HemOnc Today Breast Cancer Review & Perspective meeting to be held March 23-24, 2012 at the Hilton San Diego Bayfront. See details at HemOncTodayBreastCancer.com.
For more information:
- Mehta RS. #S1-1. Presented at: the 2011 CTRC-AACR San Antonio Breast Cancer Symposium; Dec. 6-10, 2011; San Antonio.
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