Pelabresib used as a monotherapy appears clinically beneficial in patients who have high-risk essential thrombocythemia (HR ET) and are intolerant to hydroxyurea (HU), according to a study presented at the 2023 American Society of Clinical Oncology Annual Meeting.
In this analysis of arm 4 of the MANIFEST study, lead investigator Francesco Passamonti and colleagues evaluated 20 patients with HR ET who received pelabresib monotherapy 225 mg QD. Their key end point of interest was complete hematologic response (CHR), which was defined as normalization of platelet count (≤400 x 109/L) and WBC count (≤10 x 109/L), confirmed after 1 cycle (3 weeks), and normal spleen size. Secondary end points included partial hematologic response (PHR; platelet count, 400-600 x 109/L and WBC, ≤10 x 109/L), symptom improvement (≥50% thrombosis with thrombocytopenia [TSS] reduction), and safety.
The investigators found that the majority of patients had a hematologic response (90% [18/20] unconfirmed CHR or PHR); confirmed CHR was observed in 40% of patients, and TTS reduction was observed in 86% of patients, with Hgb levels remaining stable through week 24. The investigators went on to note that the most common nonhematologic adverse events (AEs) were nausea (60%; 10% grade 3), diarrhea (35%; 5% grade 3), and dysgeusia (35%; no grade 3). No events of thrombocytopenia and no AEs of grade 4 or higher were reported.
“Preliminary results from arm 4 of the MANIFEST study suggest potential clinical benefit with [pelabresib] monotherapy in [patients] with HR ET refractory or intolerant to HU as supported by hematologic responses and symptom improvement. Safety results are consistent with the known safety profile of [pelabresib] and as expected in the underlying study population,” the researchers concluded.
Source: Passamonti F, Patriarca A, Knapper S, et al. Pelabresib (CPI-0610) monotherapy in high-risk essential thrombocythemia refractory or intolerant to hydroxyurea: preliminary results from MANIFEST study. Abstract #7019. Published for the 2023 ASCO Annual Meeting; June 2-6, 2023; Chicago, Illinois.