The following article features coverage from the San Antonio Breast Cancer Symposium (SABCS) 2018 meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Alpelisib (ALP) plus fulvestrant (FUL) consistently prolonged progression-free survival (PFS) compared with placebo plus FUL across subgroups among patients with advanced hormone receptor (HR)-positive, HER2-negative breast cancer who had PIK3CA mutations, according to data from the SOLAR-1 trial presented at the 2018 San Antonio Breast Cancer Symposium in San Antonio, Texas.1

The double-blind, phase 3 SOLAR-1 trial met its primary end point of improved PFS with ALP plus FUL treatment compared with placebo among patients with PIK3CA mutations (hazard ratio [HR], 0.65; 95% confidence interval [CI], 0.50-0.85; = .0007). This analysis provides the overall survival (OS), subgroup data, and safety information across the PIK3CA-mutant cohort.

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The SOLAR-1 trial included 341 patients with HR-positive, HER2-negative advanced breast cancer with a PIK3CAmutation who had received 1 prior line of endocrine therapy. Patients were randomly assigned to receive ALP plus FUL or placebo plus FUL with a median follow-up of 20.0 months at data cutoff. The primary end point was PFS in this cohort, and a key secondary end point was OS.

At data cutoff, the OS data were immature, but trended toward improvement with the addition of ALP, with a median OS deemed not estimable, compared with 26.9 months with placebo (HR, 0.73; 95% CI, 0.48-1.10; = .06).

In the subgroup analyses, there was a 45% decrease in risk of PFS among patients who harbored aPIK3CAmutation in their circulating tumor DNA (ctDNA) (HR, 0.55; 95% CI, 0.39-0.79), which was consistent with the primary endpoint. There was no significant difference between arms for patients without a PIK3CAmutation in ctDNA (HR, 0.80; 95% CI, 0.60-1.06).

ALP plus FUL treatment consistently prolonged PFS across most subgroups compared with placebo, including patients who had received 1 or 2 prior lines of therapy, and patients who previously received a CDK4/6 inhibitor.

ALP plus FUL was associated with greater rates of some all-grade adverse events (AEs) than placebo, with the most common including hyperglycemia (55% vs 9%), diarrhea (54% vs 11%), nausea (46% vs 20%), and rash (40% vs 6%). The most common grade 3/4 AEs in the ALP plus FUL arm compared with placebo were hyperglycemia (37% v < 1%) and rash (13% vs < 1%). AEs leading to discontinuation of therapy was similar between arms, with 3% in the ALP plus FUL group and 2% in the placebo group.

The authors concluded that these data suggest that ALP plus FUL “showed consistent clinically meaningful treatment benefit for patients with ctDNA PIK3CA-mutant status, and across subgroups.”

Read more of Cancer Therapy Advisor‘s coverage of the SABCS 2018 meeting by visiting the conference page.

Reference

  1. Juric D, Ciruelos E, Rubovszky G, et al. Alpelisib + fulvestrant for advanced breast cancer: Subgroup analyses from the phase III SOLAR-1 trial. Presented at: 2018 San Antonio Breast Cancer Symposium; San Antonio, TX; December 4-8, 2018. Abstract GS3-07.