Purpose: Brain metastases can occur in up to 50% of patients with metastatic HER2-positive breast cancer. Because patients with active brain metastases were excluded from previous pivotal clinical trials, the CNS activity of the antibody-drug conjugate (ADC), trastuzumab deruxtecan (T-DXd), is not well characterized. Experimental design: We studied how T-DXd affects growth and overall survival in orthotopic patient-derived xenografts (PDXs) of HER2-positive and HER2-low breast cancer brain metastases (BCBM). Separately, we evaluated the effects of T-DXd in a retrospective cohort study of 17 patients with stable or active brain metastases. Results: T-DXd inhibited tumor growth and prolonged survival in orthotopic PDX models of HER2 positive (IHC 3+) and HER2 low (IHC 2+ / FISH ratio < 2) BCBMs. T-DXd reduced tumor size and prolonged survival in a T-DM1 resistant HER2-positive BCBM PDX model. In a retrospective multi-institutional cohort study of 17 patients with predominantly HER2-positive BCBMs, the CNS objective response rate (ORR) was 73% (11/15) while extracranial response rate was 45% (5/11). In the subset of patients with untreated or progressive BCBM at baseline the CNS ORR was 70% (7/10). The median time on treatment with T-DXd was 8.9 (1.3-16.2) months with 42% (7/17) remaining on treatment at data cutoff. Conclusions: T-DXd demonstrates evidence of CNS activity in HER2-positive and HER2-low PDX models of BCBM and preliminary evidence of clinical efficacy in a multi-institution case series of patients with BCBM. Prospective clinical trials to further evaluate CNS activity of T-DXd in patients with active brain metastases are warranted
Purpose: Sensitivity to endocrine therapy (ET) is critical for the clinical benefit from the combination of palbociclib plus ET in hormone receptor-positive/HER2-negative (HR+/HER2-) advanced breast cancer. Bazedoxifene is a third-generation selective ER modulator and selective ER degrader with activity in preclinical models of endocrine-resistant breast cancer, including models harboring ESR1 mutations. Clinical trials in healthy women showed that bazedoxifene is well tolerated. Patients and Methods: We conducted a phase Ib/II study of bazedoxifene plus palbociclib in patients with HR+/HER2- advanced breast cancer who progressed on prior ET (N=36) (NCT02448771). Results: The study met its primary endpoint, with a clinical benefit rate of 33.3%, and the safety profile was consistent with what has previously been seen with palbociclib monotherapy. The median progression free survival (PFS) was 3.6 months (CI95% 2.0-7.2). An activating PIK3CA mutation at baseline was associated with a shorter PFS (HR = 4.4, CI95% 1.5-13, P = 0.0026) but activating ESR1 mutations did not impact the PFS. Longitudinal plasma circulating tumor DNA whole exome sequencing (WES) (N=68 plasma samples) provided an overview of the tumor heterogeneity, the sub-clonal genetic evolution and identified actionable mutations acquired during treatment. Conclusions: The combination of palbocilib and bazedoxifene has clinical efficacy and an acceptable safety profile in a heavily pre-treated patient population with advanced HR+/HER2- breast cancer. These results merit continued investigation of bazedoxifene in breast cancer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.