The Endocrine Treatment Landscape for Patients with HR+ HER2- Early-stage Breast Cancer in Germany Before the Introduction of CDK4/6 Inhibitor Therapy - A Real-World Analysis.

Introduction: While premenopausal patients with HR+ HER2- early breast cancer are treated with tamoxifen +/- ovarian suppression with a GnRH analog or an aromatase inhibitor (AI) + GnRH, the majority of postmenopausal women receive an AI due to its higher efficacy compared to tamoxifen. As the introduction of CDK4/6 inhibitors into the treatment of early-stage breast cancer with a higher risk of recurrence will probably result in a shift in the endocrine treatment landscape, the question is what treatment did potential candidates for CDK4/6 inhibitors in Germany receive before CDK4/6 inhibitors were available. Patients and Methods: As part of a retrospective multicenter analysis, anonymized data were collected of patients with HR+ HER2- early-stage breast cancer who received endocrine therapy in the period between 10/2021 and 03/2022. Potential candidates for CDK4/6 inhibitor treatment were classified into different risk cohorts using the inclusion criteria of the NATALEE and monarchE trials. Results: The data of 238 patients from 29 different centers were analyzed. While 20.6% of patients met the monarchE criteria, the subgroup which met the NATALEE inclusion criteria consisted of 46.2% of patients. 53.8% of patients did not meet the inclusion criteria for either the NATALEE or the monarchE trial. More than half of the patients did not receive chemotherapy. 28.6% of patients in the whole cohort were premenopausal. 67.6% of premenopausal women received neo-/adjuvant chemotherapy. 61.8% of premenopausal patients received tamoxifen as adjuvant endocrine therapy, 19.1% received an AI + GnRH and 10.3% were treated with tamoxifen + GnRH. Conclusion: Despite the high percentage of premenopausal patients who received aggressive treatment in the form of chemotherapy, only one third of premenopausal patients received GnRH in addition to their standard endocrine therapy. Studies carried out at a later point in time and registry studies will be necessary to see how the endocrine therapy landscape in Germany has changed following the introduction of CDK4/6 inhibitors.