Adjuvant exemestane is more effective at preventing breast cancer recurrences than tamoxifen when given with ovarian function suppression (OFS) in young women with hormone receptor–positive early breast cancer, reported Olivia Pagani, MD, Clinical Director, Breast Unit, Oncology Institute of Southern Switzerland, Bellinzona, during ASCO 2014.
In a joint analysis of the Tamoxifen and Exemestane Trial (TEXT) and the Suppression of Ovarian Function Trial (SOFT), the relative risk of developing a recurrent cancer was reduced by 28%, and the relative risk of a breast cancer recurrence was reduced by 34%, with exemestane plus OFS.
“For years, tamoxifen has been the standard hormone therapy for preventing breast cancer recurrences in young women with hormone-sensitive disease. These results confirm that exemestane with ovarian function suppression constitutes a valid alternative,” said Dr Pagani.
The 2 protocols enrolled more than 5600 premenopausal women (2672 women from TEXT and 3066 from SOFT) who had hormone receptor–positive early breast cancer. They were randomly assigned to exemestane and OFS or to tamoxifen and OFS in the TEXT study or to exemestane plus OFS, tamoxifen plus OFS, or tamoxifen monotherapy in the SOFT study. The joint analysis included 4690 women (average age, 43 years).
At a median follow-up of 5.7 years, the disease-free survival rates were 91.1% for the exemestane group and 87.3% for the tamoxifen group, corresponding to a hazard ratio (HR) of 0.72 (P = .002).
More than 96% of women were alive at 5 years. Because there were few deaths, no difference was observed in overall survival between adjuvant exemestane and tamoxifen therapy.
She noted that “some premenopausal women may have excellent prognosis with highly effective endocrine therapy alone.” A total of 1996 women in the joint analysis did not receive chemotherapy. They tended to be older (aged ≥40 years) and had smaller tumors and no nodal involvement. “More than 97% were free of breast cancer at 5 years when treated with exemestane plus ovarian function suppression,” Dr Pagani said. This compared with approximately 95% of the tamoxifen plus OFS group, for an HR of 0.41 to 0.53.
Exemestane plus OFS was also more effective than tamoxifen plus OFS for women who received chemotherapy.
Musculoskeletal complaints, osteoporosis, and fractures were more common in the exemestane group, and thrombotic or embolic events were more common in the tamoxifen group. The frequency of severe side effects and the self-reported quality of life did not differ between the groups.
Only 14% of the patients overall completely stopped the protocol-assigned treatments before 5 years—an adherence rate that exceeds that in everyday practice, said Dr Pagani. The early cessation of assigned treatment was more frequent in the exemestane group (16%) compared with the tamoxifen group (11%).
“Our findings indicate that exemestane is better than tamoxifen when given with ovarian function suppression, but longer follow-up of these young women will be important to assess survival and any long-term side effects and fertility,” Dr Pagani concluded.