Opinions of real-world clinicians on endocrine resistance in HR+/HER2- mBC: Results from the RETRACT survey of US oncologists.

Abstract

e13064 Background: Endocrine therapy (ET) is the treatment of choice in patients with metastatic breast cancer (mBC), but the benefit is limited by the inevitable development of endocrine resistance. There are few published studies evaluating the opinions of real-world clinicians concerning endocrine resistance in HR+/HER2- mBC; the RETRACT (REal-world TReatment patterns And Considerations of Toxicity in HR+/HER2- mBC) survey assessed this topic. Methods: The RETRACT survey was distributed to clinical oncologists identified using an internal database and was accessible via an online digital platform using an invitation link and individualized credentials. Responses were collected from December 2023 through April 2024. This sub-analysis descriptively summarizes the responses to 3 survey questions concerning the proper definition for endocrine resistance and whether the time intervals used in the current definition are appropriate following the introduction of CDK4/6 inhibitors. Results: Overall, 146 clinical oncologists from the USA completed the survey. Most respondents (134/144; 95%) agreed with the definition of primary endocrine resistance used in the ABC 5 international consensus guidelines, “relapse while on the first 2 years of adjuvant ET, or disease progression (PD) within the first 6 months of first-line ET for advanced BC, while on ET.” Similarly, 124/135 respondents (92%) “usually tried to exhaust all possible ET-based treatment options (with or without targeted agents) before transitioning patients to chemotherapy or antibody-drug conjugates (ADCs),” although a patient with PD in less than 6 months on CDK4/6i and ET might be best treated with chemotherapy or ADC instead. Of 133 respondents, 74 (56%) reported prescribing ET-based therapy in subsequent-line therapy after a patient has already received chemotherapy or ADC, while 32 (24%) reported prescribing ET as maintenance therapy after achieving a response to chemotherapy. Conclusions: Although most respondents agreed with the ABC 5 definition of endocrine resistance, several noted that the time intervals cited are arbitrary, and it may be worth reconsidering their current clinical relevance. Most respondents followed the recommended practice of exhausting all ET options before initiating chemotherapy or ADC. Among respondents who considered prescribing ET after chemotherapy or an ADC, circumstances frequently cited included visceral crisis post chemo response, new ET-based drug approval, or a patient who is no longer able/willing to tolerate chemotherapy. The number of respondents indicating they use ET as maintenance therapy after chemotherapy is notable, given there is no US approval for maintenance ET.