Study: Pralsentinib May Be an Effective Treatment for RET Mutation-Positive Medullary Thyroid Cancer

Pralsetinib (BLU-667) shows promise as an effective treatment for patients with advanced RET mutation-positive medullary thyroid cancer (MTC), according to new findings presented at the European Society for Medical Oncology Virtual Congress 2020.

Pralsetinib is a highly potent selective RET inhibitor that targets oncogenic RET alterations in patients with RET-positive MTC. The results included high rates of durable response and disease control as well as high rates of 18-month progression-free survival (PFS).

Patient data were taken from the ongoing ARROW study, which is being conducted at 85 sites across 13 countries. The study consists of phase 1 dose escalation that ultimately determines the recommended phase 2 dose of 400 mg of pralsetinib taken orally once daily. The phase 2 expansion cohort is defined by RET-altered tumor type and/or treatment history.

The primary objectives of phase 2 included overall response rate (ORR) and duration of response (DoR) by blinded independent central per RECIST v1.1 and safety. The study’s cutoff date was February 13, 2020. By July 11, 2019, 92 patients with RET-positive MTC were enrolled. Of these participants, 61% had M918T, 29% had cysteine rich domain, 3% had V804X, and 7% had other RET mutations.

Of the 92 patients, 53 had been previously treated with cabozantinib and/or vandetanib. For this group, the ORR was 60%, which includes a 2% complete response rate (CRR) and a 58% partial response rate (PRR). The disease control rate (DCR) was 96%. Among 19 evaluable participants who were treatment naïve, there was an observed ORR of 74%, which included a 5% CRR and a 68% PRR. The DCR for the treatment naïve group was 100%.

Neither median PFS nor the duration of response were reached. In patients previously-treated with cabozantinib or vandetanib, 94% of responders remained on treatment. Or treatment-naïve patients, 93% of responders remained on treatment.

The authors concluded that pralsetinib was well tolerated, showing potent and durable clinical activity in advanced RET mutation-positive MCT regardless of prior treatment with an approved multikinase inhibitor or RET-mutation genotype.

A total of 4% of participants discontinued therapy due to treatment-related adverse events (TRAEs). The TRAEs were primarily grade 1-2, with the most frequently reported being increased aspartate aminotransferase (34%) and anemia (24%).

Reference:

PRALSETINIB SHOWS ROBUST ACTIVITY IN PATIENTS WITH RET-ALTERED MEDULLARY THYROID CANCER [News Release] September 20, 2020; Houston, TX. https://www.esmo.org/meetings/esmo-virtual-congress-2020/meeting-resources/scientific-news/pralsetinib-shows-robust-activity-in-patients-with-ret-altered-medullary-thyroid-cancer. Accessed September 23, 2020.