CK-301-101

CK-301-101 was an open-label, multicentre, first-in-human phase 1 study of the PD-L1 antibody cosibelimab given alone to adults with advanced cancers, with a dose-escalation part followed by expansion cohorts in several tumour types (272 patients in all on the registry, which lists the study as active and no longer recruiting). Its pivotal cohorts enrolled 109 patients with cutaneous squamous cell carcinoma not suitable for curative surgery or radiotherapy, 78 with metastatic and 31 with locally advanced disease. The primary efficacy endpoint was objective response rate by independent central review using RECIST 1.1, with digital photography under WHO criteria for externally visible lesions; there was no control arm.

In the metastatic cohort, treated with 800 mg every 2 weeks, 37 of 78 patients responded (47.4 percent, 95% CI 36.0 to 59.1) at a median follow-up of 15.4 months; the median duration of response was not reached and 73 percent of responders were still responding at data cut-off. Immune-related adverse events occurred in 23 percent, grade 3 in 2.6 percent, with no grade 4 or 5 events and no treatment-related deaths (Journal for ImmunoTherapy of Cancer 2023). The current US label reports the same cohorts at a later cut: 39 of 78 (50 percent) in metastatic and 17 of 31 (55 percent) in locally advanced disease, with median duration of response not reached in either. A longer follow-up report (median 29.3 months metastatic, 24.1 months locally advanced) gave 50.0 and 54.8 percent (Journal of the American Academy of Dermatology 2026).

Cosibelimab was approved in the US in December 2024, the third PD-1 pathway antibody for this cancer after cemiplimab (EMPOWER-CSCC-1) and pembrolizumab (KEYNOTE-629).