Abstract
In MONARCH 3, continuous dosing of abemaciclib with an aromatase inhibitor (AI) conferred significant clinical benefit to postmenopausal women with HR+, HER2− advanced breast cancer. We report data for clinically prognostic subgroups: liver metastases, progesterone receptor status, tumor grade, bone-only disease, ECOG performance status, and treatment-free interval (TFI) from an additional 12-month follow-up (after final progression-free survival [PFS] readout). In the intent-to-treat population, after median follow-up of approximately 39 months, the updated PFS was 28.2 versus 14.8 months (hazard ratio [HR], 0.525; 95% confidence interval, 0.415–0.665) in abemaciclib versus placebo arms, respectively. Time to chemotherapy (HR, 0.513), time to second disease progression (HR, 0.637), and duration of response (HR, 0.466) were also statistically significantly prolonged with the addition of abemaciclib to AI. Treatment benefit was observed across all subgroups, as evidenced by objective response rate change from the addition of abemaciclib to AI, with the largest effects observed in patients with liver metastases, progesterone receptor-negative tumors, high-grade tumors, or TFI < 36 months. Extended follow-up in the MONARCH 3 trial further confirmed that the addition of abemaciclib to AI conferred significant treatment benefit to all subgroups, including those with poorer prognosis.
Highlights
In MONARCH 3, continuous dosing of abemaciclib with an aromatase inhibitor (AI) conferred significant clinical benefit to postmenopausal women with HR+, HER2− advanced breast cancer
Consistent with the primary analyses, the updated progressionfree survival (PFS) was significantly improved with the addition of abemaciclib to an AI
As evidenced by the best change in tumor size and corresponding objective response rate (ORR), all prognostic subgroups received benefit from the addition of abemaciclib to AI, with the largest effects observed in subgroups of patients with liver metastases, progesterone receptor (PgR)-negative tumors, high-grade tumors, or treatment-free interval (TFI) < 36 months (Fig. 2b)
Summary
Negative (HR, 0.427; 95% CI, 0.265–0.687), or presence of liver metastasis (HR, 0.449; 95% CI, 0.259–0.777; Fig. 1b). As evidenced by the best change in tumor size and corresponding ORR, all prognostic subgroups received benefit from the addition of abemaciclib to AI, with the largest effects observed in subgroups of patients with liver metastases, PgR-negative tumors, high-grade tumors, or TFI < 36 months (Fig. 2b). Prognostic subgroups received benefit from the addition of abemaciclib to AI These results are consistent with those observed in the overall measurable disease population. With extended follow-up in MONARCH 3, we observed that patients with bone-only disease or TFI ≥ 36 months derived meaningful PFS benefit from the addition of abemaciclib to AI which is comparable to that of other subgroups. Consistent with previously disclosed exploratory analyses, these updated subgroup analyses continue to suggest that the numerically largest benefit was observed in patients with adverse prognostic factors, such as liver metastases, PgR-negative tumors, high-grade tumors, or short TFI. The observed impact of abemaciclib in these poor prognostic subgroups in terms of extending PFS, PFS2, and TCT, as well as improving response, is both hypothesis-generating and encouraging as we await overall survival data in this population
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