“Adding ovarian suppression to tamoxifen should be considered for this population of women,” said senior author Hee Jeong Kim, MD, a breast cancer surgeon with the Asan Medical Center, Seoul, South Korea. Dr. Kim presented the data earlier this month at the annual meeting of the American Society of Clinical Oncology.
The median disease-free survival rate of 85.4% for tamoxifen plus ovarian function suppression versus 80.2% for tamoxifen alone (HR, 0.67; 95% confidence interval, 0.514-0.869; P = .0027) was consistent with recent findings from SOFT (Suppression of Ovarian Function Trial), which also showed a clear survival benefit in breast cancer events with the addition of ovarian function suppression to tamoxifen for women who remain premenopausal after chemotherapy. SOFT trial analyses of disease-free survival at 5 and 8 years demonstrated hazard ratios of 0.82 and 0.76 respectively.
Dr. Kim’s study is a post-trial follow-up of the ASTRRA trial, or the Addition of Ovarian Suppression to Tamoxifen in Young Women With Hormone-Sensitive Breast Cancer Who Remain Premenopausal or Regain Vaginal Bleeding After Chemotherapy, which randomly assigned 1,298 patients with breast cancer in a one-to-one ratio to receive tamoxifen only (n = 647) or tamoxifen plus ovarian function suppression (n = 635). The primary endpoint was disease-free survival and the secondary endpoint was overall survival.
Earlier ASTRRA analysis at 5-year follow-up had shown disease-free survival rates of 89.9% for tamoxifen plus ovarian function suppression versus 87.2% for tamoxifen alone in women with hormone-sensitive breast cancer who remained premenopausal or had premenopausal status restored after chemotherapy. Overall survival, a secondary endpoint, also favored adding ovarian function suppression (HR, 0.31; 95% CI, 0.10-0.94; P = .029). The absolute difference for disease-free survival adding ovarian function suppression at the later median follow-up of 106.4 months was 5.2%. The difference at 5 years had been 2.7%, Dr. Kim pointed out. Also, these findings were calculated from time of enrollment. When calculated from time of randomization, the disease-free survival rates were 84.1% and 78.1%, respectively, for tamoxifen plus ovarian function suppression and tamoxifen alone, with a 6.0% absolute difference (HR, 0.67; 95% CI, 0.516-0.872); P = .0025).
The benefit of adding ovarian function suppression to tamoxifen for the secondary endpoint of overall survival at 8 years (96.5% versus 95.3%) did not achieve statistical significance (HR, 0.78; 95% CI, 0.486-1.253); P = .3). “Although it’s not statistically significant, there are absolute differences between the two groups favoring tamoxifen plus ovarian function suppression,” Dr. Kim said in an interview. She pointed out also that for distant metastasis-free survival the hazard ratio was 0.71, significantly favoring tamoxifen plus ovarian function suppression. “More than 95% were still surviving at 8 years with tamoxifen plus ovarian function suppression. So, we need more events to fully evaluate the overall survival benefit.”
A study limitation, Dr. Kim acknowledged in the interview, is that safety and adverse event data were not collected. “As ovarian function suppression has been widely used in clinical practice for decades, and the side effects of its relatively short-term use were considered to be well-understood in previous studies, we focused on the oncologic efficacy of ovarian function suppression in this study,” she said.