Antonio Llombart-Cussac MD, PhD, Hospital Arnau de Vilanova, Spain, discussed extended follow-up results from the phase 2 PARSIFAL study combining the CDK4/6 (CDK4/6) inhibitor palbociclib with either fulvestrant or letrozole.

Results confirmed no major efficacy differences within treatment arms and highlighted progression within the first year of treatment may be a prognostic indicator of less favorable outcomes in this patient population.

Dr Llombart-Cussac first shared these results at the 2023 San Antonio Breast Cancer Symposium.

Transcript:

I'm Dr Antonio Llombart-Cussac, a medical oncologist based in Valencia, Spain, and it has been my honor to present at the San Antonio Breast Cancer Symposium this year the PARSIFAL-LONG, that is a sub-analysis of long-term data from the PARSIFAL study, phase 2 randomized study that compared letrozole to fulvestrant, both combined with palbociclib. It was a study that looked for what could be the optimal endocrine partner for patients with metastatic breast cancer, ER-positive, HER2-negative in the first-line setting.

This trial that was published 2 years ago in Lancet Oncology provided no differences at 3 years and now we present a follow-up at 5 years. What we observed again, was that there are absolutely no differences between the 2 arms both in progression-free survival [PFS] with a hazard ratio of 1.00 and overall survival with a hazard ratio of 0.95.

This absence of differences between the 2 arms led us to combine the arms in a single one to analyze the behavior of patients on palbociclib, first-line. We achieved a median PFS for this population of 33 months and a median overall survival of 64 months—that's very close, very similar to what we have observed in pivotal studies with the other CDK4/6 inhibitors.

The interesting issue is that we have also done some exploratory analysis on prognostic factors and the strongest prognostic factor for survival appears to be the median duration of progression-free survival, so those patients that were progressed within the first 12 months did very bad. In fact, the survival for patients progressing within the first 12 months is 18 months. On the other hand, the ones that progressed after 12 months, overall survival is superior at 20 to 29 months, indicating that this 12-month cutoff could be used in the future to identify the patients for which probably we can start to consider as non-sensitive to endocrine therapies, and that could be moved forward quicker to more aggressive or different approaches.

Source:

Llombart-Cussac A, Pérez-García JM, Bellet- Ezquerra M, et al. PARSIFAL-LONG: Extended follow-up of hormone receptor-positive /HER2-negative advanced breast cancer patients treated with fulvestrant and palbociclib vs. letrozole and palbociclib in the PARSIFAL study. Presented at the 2023 San Antonio Breast Cancer Symposium. December 4-9, 2023. Abstract RF01-03