Palbociclib Shows Clinical Benefit in Black and Hispanic Patients with HR+ Breast Cancer

Claudine Isaacs, MD

Responses from Black and Hispanic patients with hormone receptor (HR)–positive, HER2-negative advanced breast cancer who received palbociclib (Ibrance) plus endocrine therapy were consistent with outcomes seen in overall study populations, supporting the continued use of this combination among this patient population, according to a pooled efficacy and safety analysis presented at the 2021 San Antonio Breast Cancer Symposium (SABCS).

The relatively small proportion of Black and Hispanic patients in key clinical trials that led to the approval of palbociclib across multiple indications in advanced breast cancer motivated the research team to look further at this population.

“This post-hoc analysis of the PALOMA trials evaluated the efficacy and safety of palbociclib plus endocrine therapy in Black and Hispanic patients,” Claudine Isaacs, MD, professor of medicine and oncology and Clinical Breast Cancer Program Lead at Lombardi Comprehensive Cancer Center at Georgetown University, said in a recorded presentation of the findings. “Approximately 10% of the PALOMA-2 and PALOMA-3 patient populations self-identified as Black or Hispanic.”

Previously reported data from the placebo-controlled, phase 3 PALOMA-2 (NCT01740427) and PALOMA-3 (NCT01942135) clinical trials, which served as the efficacy analysis for this dataset, demonstrated a significant improvement in median progression-free survival (PFS) with a manageable safety profile when patients were treated with a palbociclib-containing regimen. The safety analysis also included data from the phase 2 PALOMA-1 trial (NCT00721409).

In PALOMA-1 and PALOMA-2, postmenopausal patients received palbociclib plus letrozole vs letrozole alone or with placebo, respectively, as frontline treatment for HR-positive, HER2-negative advanced breast cancer. In PALOMA-3, pre- or postmenopausal patients with disease progression after endocrine therapy were treated with fulvestrant (Faslodex) and either placebo or palbociclib.

The median PFS in 65 self-identified Black or Hispanic patients treated on PALOMA-2 was 27.4 months vs 13.8 months for the palbociclib and placebo arms, respectively (HR, 0.61; 95% CI, 0.31-1.20). In the 48 self-identified Black or Hispanic patients treated on PALOMA-3, corresponding medians were 11.1 and 1.9 months, respectively (HR, 0.56; 95% CI, 0.28-1.14).

Overall survival results were available for the patients treated on the PALOMA-3 trial, showing a greater benefit with palbociclib at 35.6 months vs 21.0 months with placebo (HR, 0.48; 95% CI, 0.23-0.97).

The safety analysis of all 3 trials revealed a toxicity profile for 120 self-identified Black and Hispanic patients that was consistent with previously reported data in the intention-to-treat (ITT) population. The most common grade 3/4 hematologic adverse effects (AEs) were neutropenia (57.7%), leukopenia (24.4%), and anemia (3.8%), which were all similar to the rates in the overall population (65.4%, 26.7%, and 4.6%, respectively).

All-grade non-hematologic AEs in the intent-to-treat (ITT) and subgroup analysis included infections (50.0% vs 54.7%, respectively), fatigue (39.7% vs 39.2%), nausea (38.5% vs 34.2%), constipation (30.8% vs 19.2%), arthralgia (29.5% vs 25.6%), cough (26.9% vs 21.6%), stomatitis (17.9% vs 28.9%), and alopecia (16.7% vs 25.9%).

Dose reductions resulting from AEs occurred in 37.2% of Black and Hispanic patients treated with palbociclib and was similar to the rates observed in the ITT population across all 3 trials (range, 39.4%-42.2%). Dose interruptions or delays occurred in 60.3% of Black and Hispanic patients treated with active therapy, which was slightly lower than the same rate in the ITT population (71.4%).

Patient characteristics were detailed for the PALOMA-2 and PALOMA-3 trials and were well-balanced between groups. Of the 66 self-identified Black or Hispanic patients treated on PALOMA-2, 47 received active therapy and 18 received placebo. Median patients ages were 58 years (range, 35-89) and 54 years (range, 39-67), respectively. More patients treated with palbociclib had visceral disease (61.7% vs 50.0%), lung involvement (51.1% vs 22.2%), and de novo disease (44.7% vs 22.2%) whereas fewer had received prior systemic therapy (55.3% vs 77.8%) than those in the placebo group. Of the 48 self-identified Black or Hispanic patients treated on PALOMA-3, 29 received active therapy and 19 received placebo; median patient age was 57 years in both groups.

Palbociclib is a first-in-class CDK4/6 inhibitor approved for use in combination with an aromatase inhibitor or fulvestrant in patients with hormone receptor–positive, HER2-negative advanced breast cancer.

“These findings support the continued use of palbociclib plus endocrine therapy for women hormone receptor–positive, HER2-negative advanced breast cancer in Black and Hispanic patients,” Isaacs concluded.

Reference

1. Isaacs C, Mahtini R, Lynce F, et al. Efficacy and safety of palbociclib plus endocrine therapy in Black and Hispanic patients with hormone receptor positive/human epidermal growth factor receptor 2-negative advanced breast cancer (HR+/HER2- ABC) participating in the PALOMA trials. Presented at: San Antonio Breast Cancer Symposium. December 7-10, 2021. San Antonio, TX. Abstract P1-18-13.