No Significant Differences at 5 Year Follow-Up Between Palbociclib-Based Treatment Regimens

Results from the PARSIFAL-LONG study investigating endocrine-sensitive hormone receptor-positive/HER2-negative (HR+/HER2-) advanced breast cancer demonstrated the efficacy of 2 combined option therapies, palbociclib (Ibrance; Pfizer) plus letrozole (Femara; Novartis) and palbociclib plus fulvestrant (Faslodex; Hikma), as first-line treatments for metastatic breast cancer. The study found no significant differences in progression-free survival (PFS) and overall survival (OS) between the 2 treatments. The trial results were presented at the 2023 San Antonio Breast Cancer Symposium (SABCS) in Texas.

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PARSIFAL-LONG is the follow-up trial to PARSIFAL, which explored the optimal endocrine agent—letrozole vs fulvestrant—to combine with palbociclib in patients with untreated, endocrine-sensitive, HR+/HER2- advanced breast cancer in the first-line setting. The trial was unsuccessful in demonstrating an improvement in PGS of palbociclib plus fulvestrant over palbociclib plus letrozole, with a median follow-up of 2.7 years. OS data were immature at data cutoff.

PARSIFAL-LONG is the extended efficacy assessment of the PARSIFAL study with a median follow-up of 5 years. The primary goals were to assess the OS, the extended PFS, the OS from the combined groups, and the post-progression efficacy of treatment between the palbociclib plus letrozole and palbociclib plus fulvestrant groups. A total of 389 patients with HR+/HER2- advanced breast cancer were enrolled, representing 80.5% of the total patients initially enrolled in PARSIFAL. Approximately 22.1% of patients (n = 86) had a progression within the first year of treatment, with a median OS of 24 months. The remaining 77.9% of patients (n= 303) were progression-free on palbociclib-based regiments at 12 months, demonstrating an improved median OS of 81.5 months.

The patients who experienced a progression during the 5-year follow-up were assessed based on the time that they progressed: those who progressed within the first year had an OS of 18 months compared to those who progressed after a year, who had an OS of 27 months.

The study found no significant differences in PFS and OS when palbociclib was paired with either letrozole or fulvestrant (median follow-up of 59.7 months). Due to the lack of difference between the groups, the combined median PFS between the groups was 33.2 months (95% CI, 27.7-39.5 months) and the combined median OS was 65.4 months (95% CI, 57.8-72.0 months).

"Upon combining the 2 arms, our OS and PFS values align comparably with other CDK4/6 inhibitors," said Antonio Llombart-Cussac, MD, PhD, head of the oncology department at Arnau de Vilanova Hospital and medical senior scientific lead at MEDSIR, when presenting the results. "Early progression with a palbociclib-based regimen serves as a robust early clinical biomarker for survival."

Reference

MEDSIR. Prolonged PARSIFAL study shows no distinct differences at 5 years between palbociclib-letrozole and palbociclib-fulvestrant in HR[+]/HER2[-] advanced breast cancer. News release. December 6, 2023. Accessed December 7, 2023. https://www.prnewswire.com/news-releases/prolonged-parsifal-study-shows-no-distinct-differences-at-5-years-between-palbociclib-letrozole-and-palbociclib-fulvestrant-in-hrher2--advanced-breast-cancer-302007622.html