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Press Release: PARSIFAL-LONG at San Antonio Breast Cancer Symposium

Updated: Dec 18, 2023

Prolonged PARSIFAL study shows no distinct differences at 5 years between palbociclib-letrozole and palbociclib-fulvestrant in HR[+]/HER2[-] advanced breast cancer

  • PARSIFAL-LONG, the 5-year extended follow-up of the PARSIFAL study, showed a progression-free survival of 33.2 months and an extended overall survival of 65.4 months

  • No significant differences were found in terms of progression-free survival or overall survival when first-line palbociclib was combined with either letrozole or fulvestrant in patients with metastatic HR[+]/HER2[-] breast cancer

  • MEDSIR had a significant participation at the 46th San Antonio Breast Cancer Symposium conference by presenting 5 studies including PARSIFAL-LONG, DEBBRAH cohort 5, ATRACTIB, PARALEAL and MiRaDor.

SAN ANTONIO, TX, December 6, 2023 – MEDSIR today announced 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. 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).

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.


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.


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.


Founded in 2012, MEDSIR works closely with its partners to drive innovation in oncology research. Based in Spain and the United States, the company manages all aspects of clinical trials, from study design to publication, utilizing a global network of experts and integrated technology to streamline the process.

The company offers proof-of-concept support and a strategic approach that helps research partners experience the best of both worlds from industry-based clinical research and investigator-driven trials. To promote independent cancer research worldwide, MEDSIR has a strategic alliance with Oncoclínicas, the leading oncology group in Brazil with the greatest research potential in South America. Learn how MEDSIR brings ideas to life:


San Antonio Breast Cancer Symposium (SABCS) hosts about 10,000 clinicians and scientists from all over the world and is the largest and most prestigious scientific gathering on breast cancer research.




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