top of page


PARSIFAL clinical trial results presented at ASCO Annual Meeting

Updated: Aug 13, 2021

Despite having a virtual format, this year’s edition of ASCO was still a success and managed to join oncologists and clinical scientists from all over the globe to share knowledge and the latest advances in their respective studies. Dr. Antonio Llombart, Head of the Medical Oncology Service at the University Hospital Arnau de Vilanova (Valencia, Spain) was among the speakers invited to give an oral presentation reporting the results of the PARSIFAL trial; a multi-center, randomized, open-label phase II study that explored the optimal endocrine agent to combine with palbociclib as initial therapy for patients with endocrine-sensitive, ER[+]/HER2[-] advanced breast cancer (ABC).

Researchers from 48 hospitals in 7 different countries randomized a total of 486 patients to receive palbociclib with either fulvestrant or letrozole. Randomization was stratified according to the type of disease presentation (de novo vs recurrent) and the presence of visceral involvement (yes vs no). The primary endpoint was investigator-assessed progression-free survival (PFS), determined by Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1).

These results have been anticipated with great interest in the oncology community, to determine the best endocrine agent to combine with palbociclib in this setting after the results of FALCON, PALOMA-2 and MONALEESA-3 trials” said Dr. Llombart, co-leader of this study.

Although fulvestrant–palbociclib demonstrated significant antitumor activity, this study failed to identify an improvement in PFS of this treatment over letrozole–palbociclib in patients with endocrine-sensitive, ER[+]/HER2[-] ABC. No clinically relevant differences in PFS were observed across all pre-specified subgroups either. Both regimens were extremely well tolerated. Out of neutropenia, Grade 3 or greater adverse events were uncommon in both Arms A & B and no new safety signals were identified.

We believe that the results of PARSIFAL trial support non-steroidal aromatase inhibitor (NSAI) use as the preferred endocrine partner for CDK4/6 inhibitors as initial therapy for this patient population” pointed out Dr. Javier Cortés, Head of the Breast Cancer Program at IOB Institute of Oncology (Madrid & Barcelona, Spain) and scientific co-leader of this trial.

"Still, the use of fulvestrant instead of NSAI in combination with CDK4/6 inhibitors is a consistent option for endocrine-sensitive patients who are intolerant to NSAI, as well as single-agent in endocrine-sensitive patients with indolent disease or not candidates for CDK4/6 inhibitors", said Dr. Llombart.

You can now read the abstract and watch the results of the PARSIFAL trial presented at ASCO following this link.

For more information, do not hesitate to visit the PARSIFAL clinical trial or get in touch with us at




bottom of page