The association between age, toxicity and outcomes of abemaciclib treatment in HR+/HER2- metastatic breast cancer.

e13062 Background: The efficacy and safety of abemaciclib in patients (pts) with HR+/HER2− metastatic breast cancer (MBC) was demonstrated in the MONARCH clinical trials; however, real-world evidence is lacking, particularly in elderly pts. The dose reduction strategy used in the MONARCH trials has been shown to be an effective way of managing toxicity without compromising survival. Here, we provide real-world data on the efficacy and safety of abemaciclib treatment, focusing also on elderly pts with HR+/HER2− MBC and the association between abemaciclib dose reduction and survival. Methods: The efficacy and safety of abemaciclib in patients (pts) with HR+/HER2− metastatic breast cancer (MBC) was demonstrated in the MONARCH clinical trials; however, real-world evidence is lacking, particularly in elderly pts. The dose reduction strategy used in the MONARCH trials has been shown to be an effective way of managing toxicity without compromising survival. Here, we provide real-world data on the efficacy and safety of abemaciclib treatment, focusing also on elderly pts with HR+/HER2− MBC and the association between abemaciclib dose reduction and survival. Results: The median age of 134 pts was 62 yrs (IQR, 54-71), with 40 pts (29.9%) older than 70 yrs. Median rwPFS (mrwPFS) with abemaciclib + endocrine therapy in the ≥70 vs <70 age group was 15 vs 17 months (HR:1.1, 95% CI 0.70-1.76; p=0.65) and median OS (mOS) was 25 vs 34 months (HR:1.4, 95% CI 0.82-2.39, p=0.21). The most common rwAEs are shown (Table). Abemaciclib dose reductions occurred in 40% of pts ≥70 yrs of age compared to 28% of younger pts (χ2 (1)=1.98; p=0.22). There was no difference in mrwPFS between pts who had a dose reduction and those who did not (mrwPFS 15 vs 17 months (HR: 1.03, 95% CI 0.65-1.63, p=0.91) and mOS 28 vs 30 months (HR: 1.16, 95% CI 0.68-1.99; p=0.58)). Conclusions: The results of our study support the efficacy and safety of abemaciclib treatment in pts with HR+/HER2- MBC in real-world clinical practice. Age did not appear to be an important factor associated with higher rates of toxicity and similar efficacy of abemaciclib was demonstrated in the elderly pts population compared to younger pts. Importantly, abemaciclib dose reductions did not compromise survival. Clinical trial information: ERIDNPVO-0060/2022. Table: see text