On December 6, 2023 MEDSIR reported the results from the PARSIFAL-LONG study, a 5-year extended follow-up of the PARSIFAL study on endocrine-sensitive hormone receptor-positive/HER2-negative advanced breast cancer, demonstrating the effectiveness of two combined option therapies (palbociclib-letrozole and palbociclib-fulvestrant) as first-line treatments for metastatic breast cancer (Press release, MedSIR, DEC 6, 2023, View Source;advanced-breast-cancer-302007622.html [SID1234638205]). With a median follow-up of 59.7 months, the study found no significant differences in progression-free survival and overall survival when palbociclib was paired with either letrozole or fulvestrant. Given that there was no difference between groups, they were combined, and it was determined that the median progression-free survival was 33.2 months (95%CI, 27.7-39.5), and the median overall survival was 65.4 months (95%CI, 57.8-72.0).

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PARSIFAL explored the optimal endocrine agent (letrozole vs fulvestrant) to combine with palbociclib in patients with untreated, endocrine-sensitive, hormone receptor positive/HER2-negative advanced breast cancer in the first-line setting. The trial failed to demonstrate an improvement in progression-free survival of palbociclib-fulvestrant over palbociclib-letrozole, with a median follow-up of 2.7 years. At data cutoff, overall survival data were immature.

PARSIFAL-LONG extended the efficacy assessment of the PARSIFAL study with a median follow up of 5.0 years. It included a total of 389 patients, which represents 80.5% of all patients initially enrolled in PARSIFAL. Among them, 86 patients (22.1%) had a progression within the first year of treatment (early progressors), with a median overall survival of 24 months. The remaining 303 patients (77.9%) were progression-free on palbociclib-based regiments at 12 months and showed an improved median overall survival of 81.5 months.

Patients who experienced a progression during the 5-year follow-up were then assessed based on the time that they progressed. Those who progressed within the first year had an overall survival of 18 months compared to 27 months for patients that progressed after a year (hazard ratio, 0.67, 95%CI, 0.51-0.90, p=0.007), indicating that early progression (<12 months) on a palbociclib-based regimen is a strong predictor for overall survival.

These results were presented at the 46th annual San Antonio Breast Cancer Symposium by Dr. Antonio Llombart-Cussac, Head of the Oncology Department at Arnau de Vilanova Hospital and Medical Senior Scientific Lead at MEDSIR, a Spanish company specialized in the strategic design of independent clinical research. This year, MEDSIR had a significant participation at the conference by showcasing 5 studies including PARSIFAL-LONG, DEBBRAH, ATRACTIB, PARALEAL and MiRaDor. He emphasized, "Upon combining the two arms, our overall survival and progression-free survival values align comparably with other CDK4/6 inhibitors." Dr. Llombart-Cussac further noted, "Early progression with a palbociclib-based regimen serves as a robust early clinical biomarker for survival."

A total of 389 patients from 32 of the original 47 sites participated in this trial, which is the only study for a CDK4/6 regimen that recruited patients exclusively across European countries including Spain, France, Italy, Great Britain, Deutschland and Czech Republic.

The PARSIFAL-LONG study provides valuable insights, expanding the understanding of the magnitude of benefit and further reinforces the evidence supporting palbociclib in combination with endocrine therapy as a first-line treatment for patients with hormone receptor-positive/HER2-negative metastatic breast cancer.

ABOUT PARSIFAL-LONG

PARSIFAL-LONG, is a 5-year extended follow-up of the PARSIFAL study. In this analysis, the primary goal was to assess the overall survival, or the time from enrollment to death from any cause, between the two groups (palbociclib-letrozole vs palbociclib-fulvestrant). In addition, the study assessed the extended progression-free survival (time from randomization until the disease getting worse), the overall survival from the combined groups, and the post progression effectiveness or the how well the treatment worked in terms of the time from disease worsening after the first treatment to the passing of any cause. As exploratory analysis, this extended follow-up also aimed to determine if having an early progression (the disease getting worse in under 12 months while on treatment) could be an indicator of resistance to therapy.

ABOUT BREAST CANCER

Breast cancer is the second most common cause of death from cancer in women in the United States. Metastatic breast cancer causes the vast majority of deaths from the disease. In 2023, it is estimated that there will be 297,790 new cases of female breast cancer. The breast cancer subtype HR[+]/HER2[-], whose tumors express hormone receptors (HR[+]), but do not express HER2 protein (HER2[-]), is the most common subtype with an age-adjusted rate of 87.2 new cases per 100,000 women, based on 2016–2020 cases, according to the US National Cancer Institute.