Blueprint Medicines reported Sunday data from an early-stage study of BLU-667 in patients with RET-altered solid tumours, with the experimental drug showing "broad anti-tumour" activity. Data for the oral therapy, which is a selective inhibitor targeting oncogenic RET fusions and mutations, were presented at the American Association for Cancer Research (AACR) annual meeting.

The ARROW study is designed to evaluate the safety and tolerability of once-daily BLU-667 in multiple ascending doses in adults with RET-altered non-small-cell lung cancer (NSCLC), medullary thyroid cancer (MTC) and other advanced solid tumours. As of the data cutoff date of April 6, 40 patients with RET-altered tumours were evaluable for response assessment, including 14 patients with NSCLC, 25 patients with MTC and one patient with papillary thyroid cancer.

Results showed that across all evaluable patients, the preliminary overall response rate (ORR) was 45 percent, with responses observed in patients previously treated with multi-kinase therapy, immunotherapy and chemotherapy. Specifically, 50 percent of patients with NSCLC had a partial response, while in subjects with MTC, the ORR was 40 percent, including one complete response and nine partial responses. In addition, the data showed radiographic tumour reductions in 84 percent of patients with RET-altered solid tumours with measurable target lesions.

Study investigator Vivek Subbiah remarked "this ongoing Phase I study has shown proof-of-concept of this selective RET inhibitor," adding "although it's very early in clinical testing, we observed promising antitumor activity in NSCLC and MTC." Subbiah noted that "current therapies for RET-altered cancers are restricted to multikinase inhibitors and chemotherapy, which are nonspecific and display significant off-target toxicity."

Meanwhile, Blueprint Medicines' chief medical officer Andy Boral commented "based on these data, we are excited to rapidly advance the global expansion portion of the trial, which will further evaluate an optimised dose of BLU-667 across a broad patient population with a focus on durability of activity."

Other RET inhibitors under development include Loxo Oncology's LOXO-292, with results announced last year showing that two patients with RET-fusion lung cancer treated with the experimental drug achieved a partial response.

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