Updated results from the SOFT and TEXT clinical trials, conducted in premenopausal women with hormone sensitive early breast cancer, show fewer recurrences and improved survival for young breast cancer patients treated with ovarian suppression, with patients at higher risk of recurrence experiencing the most benefit.
Very young women with hormone sensitive breast cancer are a group found to have a higher risk of recurrence. Tamoxifen has been the standard adjuvant hormonal treatment for premenopausal women with hormone-sensitive breast cancer. For many years it has been uncertain if adding treatment to suppress ovarian function to tamoxifen would significantly improve outcomes.
The SOFT and TEXT trials were designed to determine the value of adding ovarian suppression to tamoxifen in reducing breast cancer recurrence, and to determine whether further reduction in recurrence would be achieved by using an aromatase inhibitor exemestane in combination with ovarian suppression. Aromatase inhibitors are standard treatment in postmenopausal women but require suppression of estrogen produced by the ovaries to be effective in premenopausal women.
In the SOFT study, adding ovarian function suppression to tamoxifen significantly decreased the relative risk of disease-free survival events by 24% versus tamoxifen-alone in the overall population after 8 years median follow-up, resulting in a 4.2% absolute benefit at 8 years. The absolute benefit was larger in women who remained premenopausal after receiving chemotherapy before starting ovarian suppression. The clinical benefit was particularly clear in women under age 35, with an 8.6% absolute benefit at 8 years. Further reduction in recurrence was seen with the use of the aromatase inhibitor exemestane plus ovarian function suppression. Improvement in overall survival is now seen at 8 years, with the use of ovarian function suppression, particularly in women who remained premenopausal after receiving adjuvant chemotherapy. However, the frequency of side effects was higher than reported for treatment with tamoxifen alone.
After a median follow-up of 9 years, the combined analysis of the SOFT and TEXT studies confirmed statistically significant improvements in disease outcomes with exemestane versus tamoxifen used in combination with ovarian suppression. Adjuvant exemestane plus ovarian function suppression, compared with tamoxifen plus ovarian function suppression, showed sustained absolute improvements in disease-free survival and freedom from distant recurrence of 4.0% and 2.1% at 8 years, respectively. Women with HER2-negative breast cancer experienced the most clinical benefit, especially those who also received adjuvant chemotherapy due to a higher risk of recurrence. In these higher-risk groups, absolute improvements in disease-free survival and freedom from distant recurrence were 7-9% and 5-7% across SOFT and TEXT, respectively with exemestane plus ovarian suppression. No difference in overall survival after 9 years median follow-up was observed when comparing the two groups of women who were all treated with ovarian suppression.
The overall results of the SOFT and TEXT trials were published in the New England Journal of Medicine. More than 5,700 women participated in SOFT and TEXT worldwide, including 489 from Australia and New Zealand. The trials were conducted in Australia and New Zealand by Breast Cancer Trials (BCT). Associate Professor Prue Francis chaired the International Steering Committee responsible for the SOFT and TEXT clinical trials and was the senior author of the publication of the results. Associate Professor Francis is also the Chair of the BCT Scientific Advisory Committee.
“These trial results will change the management of breast cancer in young women with oestrogen receptor positive early breast cancer, leading to fewer recurrences and improved overall survival. The SOFT and TEXT trials are important examples of how research conducted by a cancer clinical trials group at a national and international level, can contribute to improving cancer outcomes,” said Associate Professor Francis.
Breast Cancer Trials (BCT) is the largest, independent oncology clinical trials research group in Australia and New Zealand and has conducted a national clinical trials research program for the treatment, prevention and cure of breast cancer for 40 years. The research program involves almost 800 members at 101 leading medical institutions in Australia and New Zealand. More information about BCT and its research program visit www.breastcancertrials.org.au.