The STP trials are complementary studies designed to answer three open questions concerning adjuvant treatment for premenopausal patients with endocrine responsive disease: What is the role of ovarian function ablation/ suppression (OFS)? What is the role of aromatase inhibitors? What is the role of chemotherapy? We know that chemotherapy, tamoxifen and OFS are individually effective adjuvant treatment modalities in women under 50 years of age with estrogen receptor-positive breast cancer [5, 6]. The addition of 5 years of tamoxifen to adjuvant chemotherapy in this group results in an additional approximately 40% reduction in the odds of recurrence or death [7, 8]. These data suggest that adjuvant combination chemo-endocrine strategies can improve results over single modality treatments.
Conclusive data on the best approaches to treat this population are scarce because positive results for chemotherapy in the 1970s (mainly for women in their forties) and misleading overview reports on tamoxifen (claimed to be ineffective in younger women) in the 1980s and 1990s, inhibited evaluation of endocrine therapies for younger women. Adjuvant treatment of choice for individual premenopausal women with endocrine responsive disease is largely based upon assessment of risk of relapse and physician's perception on the relative role of endocrine versus cytotoxic approaches. To offer a randomized clinical trial to define a better adjuvant treatment for premenopausal women with endocrine responsive disease, three tailored treatment investigations are being conducted globally by the IBCSG through the Breast International Group and the North American Breast Intergroup.
The Suppression of Ovarian Function Trial (SOFT: IBCSG 24-02) is designed to determine the role of OFS and the role of aromatase inhibitors for women who remain premenopausal after surgery alone or after completion of adjuvant and/or neoadjuvant chemotherapy.
The Tamoxifen and Exemestane Trial (TEXT: IBCSG 25-02) is designed to determine the role of aromatase inhibitors for women who receive OFS (with triptorelin) from the start of adjuvant therapy. Chemotherapy, if given, should be started with the triptorelin and followed by the tamoxifen or exemestane. Use of chemotherapy is by investigator/patient choice or by randomized assignment in the PERCHE trial.
The Premenopausal Endocrine Responsive Chemotherapy Trial (PERCHE: IBCSG 26-02) is designed to determine the role of chemotherapy. It features randomization either to OFS plus tamoxifen or exemestane, or to chemotherapy plus OFS plus tamoxifen or exemestane. Women for whom the role of adding chemotherapy to 'complete estrogen blockade' is uncertain should be offered PERCHE.
As of June 30, 2005, 164 participating centers from North America, Europe, Australia, South America, and Africa have randomized patients on these trials, including 243 on SOFT, 432 on TEXT, and 10 on PERCHE. The total required sample size is 3,000, 1,845 and 1,750 patients, respectively.