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Exelixis Begins Trial of Zanzalintinib With Keytruda in PD-L1-Positive Head and Neck Cancer

NEW YORK – Exelixis on Monday said it began a Phase II/III trial of its tyrosine kinase inhibitor zanzalintinib as a treatment for patients with PD-L1-positive head and neck cancer.

In the STELLAR-305 trial, Exelixis researchers will evaluate zanzalintinib and Merck's checkpoint inhibitor Keytruda (pembrolizumab) compared to placebo and Keytruda as a first-line treatment in about 500 patients with previously untreated, recurrent, or metastatic head and neck cancer. A blinded independent radiology committee will compare patients' progression-free survival and overall survival in the treatment arms. Secondary endpoints in the trial include investigator-assessed progression-free survival, objective response rate, and duration of response.

"We are excited to progress zanzalintinib … into this population of patients who otherwise are relegated to immunotherapy plus chemotherapy, but may benefit from a chemo-free option," Exelixis Chief Medical Officer Amy Peterson said in a statement.

An investigator-initiated Phase II trial of Exelixis' approved kinase inhibitor Cabometyx (cabozantinib) with Keytruda in recurrent and metastatic head and neck squamous cell carcinoma provided the rationale for STELLAR-305.

That trial showed an overall response rate of 54 percent and an overall clinical benefit rate of 91 percent on Cabometyx-Keytruda. The progression-free survival rate was 54 percent at a median follow-up of 10.6 months, and the one-year overall survival rate was 68.4 percent. When broken down by PD-L1 expression status, patients with a PD-L1 combined positive score of 20 or more had a one-year overall survival rate of 83.6 percent and median overall survival of 32.9 months, compared to a one-year overall survival rate of 54.9 percent and median overall survival of 14.6 months for those with a PD-L1 combined positive score under 20.

The Alameda, California-based company is also comparing the activity of zanzalintinib plus Roche's checkpoint inhibitor Tecentriq (atezolizumab) against Bayer's multi-kinase inhibitor Stivarga (regorafenib) in a Phase III trial involving patients with mismatch repair-proficient, microsatellite stable colorectal cancer.