In Reply In recent letters to the editor regarding the article, “The Effect of Abemaciclib Plus Fulvestrant on Overall Survival in Hormone Receptor–Positive, ERBB2-Negative Breast Cancer That Progressed on Endocrine Therapy—MONARCH 2: A Randomized Clinical Trial,”1 it was proposed that it is inappropriate to examine graphical overall survival (OS) results in subgroups and that no significant interaction tests were provided. We respectfully refer to the Results: Overall Survival section of the article where it was stated that interaction tests for site of disease (visceral, bone only, and other) and endocrine resistance (primary and secondary) were not statistically significant. Given that the OS for the intent-to-treat population was statistically significant, we concluded that all patients benefit from the addition of abemaciclib to fulvestrant. We concur that the interaction test is the pivotal test for determining if treatment effects are significantly different between patient subgroups and if, indeed, all patient subgroups benefit from the experimental treatment compared with control. However, even without a statistically significant interaction, examination of clinically relevant subgroups (and in this case, stratification factors) can provide important data for clinical decision-making.2-5 In the case of patients with visceral disease or primary endocrine resistance, physicians may consider either endocrine-based therapy or chemotherapy. It may be important to confirm not only that patients in these subgroups benefit from the addition of abemaciclib to fulvestrant, but also that the effect is meaningful in terms of early separation of the curves and difference at the medians. That is why analysis of OS was preplanned in these subgroups.
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Sledge GW, Frenzel M. Analysis of Overall Survival Benefit of Abemaciclib Plus Fulvestrant in Hormone Receptor–Positive, ERBB2-Negative Breast Cancer—Reply. JAMA Oncol. 2020;6(7):1122–1123. doi:10.1001/jamaoncol.2020.1518
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