IBCSG has focused on clinical trials designed to tailor treatments to breast cancer patient populations to improve prognosis, minimize morbidity, and enhance quality of life. Some selected examples are cited below:

• The group pioneered research demonstrating the role of accurately-determined steroid hormone receptor status (estrogen and/or progesterone receptor) of the tumor and menopausal status of the patient as critical features that impact treatment selection. Early studies demonstrated the importance of hormonal therapy against disease expressing hormone receptors, the hormonal effects of chemotherapy for biologically-defined premenopausal women, and the importance of chemotherapy against disease that does not express hormone receptors.
• IBCSG conducted the BIG 1-98 study, which enrolled over 8000 women and demonstrated improved outcomes with the aromatase inhibitor, letrozole, compared with tamoxifen for postmenopausal women with hormone receptor positive disease.
• IBCSG 23-01 showed that axillary dissection did not improve disease control compared with no axillary dissection for patients with micrometastases in sentinel lymph nodes, thus avoiding adverse side effects of the more extensive surgery for many women.
• The SOLE (Study of Letrozole Extension) trial demonstrated that for postmenopausal women with node-positive disease who had completed 4-6 years of prior post-surgical hormonal therapy, using up to 5 more years of intermittent letrozole therapy (with 3 months of planned treatment interruption) had similar disease control with less toxicity compared with continuous letrozole administration.
• The CALOR (Chemotherapy Adjuvant for Local Or Regional recurrence) trial showed that using chemotherapy after resecting loco-regional recurrences improved disease control for recurrences that were hormone receptor negative, but not for those that were hormone receptor positive  
• The PANACEA study provided proof-of principle evidence that immunotherapy, specifically PD-1 inhibition like pembrolizumab, can help overcome trastuzumab resistance that is seen in patients with metastatic HER2-positive breast cancer.
  In addition, quantification of tumor infiltrating lymphocytes (TILs) seems to be a meaningful way for us to identify those who would benefit most from an immunotherapeutic approach.
• The SOFT (Suppression of Ovarian Function Trial) and TEXT (Tamoxifen and Exemestane Trial) studies established new standards of care for premenopausal women with higher-risk hormone responsive disease, demonstrating improved control of disease recurrence with ovarian function suppression plus the aromatase inhibitor, exemestane, compared with either tamoxifen alone, or tamoxifen plus ovarian function suppression.
• SOFT and TEXT also demonstrated that patients with lower-risk disease achieved excellent disease control with tamoxifen alone.
• ETOP IBCSG Partners Foundation is currently conducting the POSITIVE (Pregnancy Outcome and Safety of Interrupting Therapy for women with endocrine responsIVE breast cancer) study, in collaboration with BIG and NABCG, to determine whether young women with hormone receptor positive disease who wish to have a child but are receiving hormonal treatment can safely temporarily interrupt anti-cancer therapy in order to attempt pregnancy. Enrolment of 500 patients to this unique, patient-oriented study has been completed in early 2020.