Sun Pharmaceutical Industries will present long-term follow-up results from the pivotal trial of UNLOXCYT (cosibelimab-ipdl) in advanced cutaneous squamous cell carcinoma (aCSCC) at ESMO 2026 in Madrid. The data extend a study that supported the drug’s 2024 US approval, and they speak to a question that matters for any cancer therapy: whether early responses last.
The abstract expands the pivotal CK-301-101 analysis to 205 patients across three cohorts — metastatic disease treated every two weeks, locally advanced disease treated every two weeks, and metastatic disease treated every three weeks. Across the cohorts, objective response rates ranged from 44% to 53%, and complete-response rates from 17% to 34%. Among patients who responded, the estimated probability of remaining in response at two years ranged from 69% to 82%. The company describes the data as one of the largest prospective studies of aCSCC patients treated with a single PD-(L)1 inhibitor.
Durability and complete responses
The headline for clinicians is durability. In the locally advanced cohort, 34% of patients achieved a complete response — the disappearance of detectable tumour — and the median duration of response was not reached, with the estimated two-year response probability at 82%. In the metastatic cohorts, complete-response rates were 17% and 21%, with response probabilities at two years of about 69% and 73%.
Those figures are consistent with the pattern the drug showed at approval, when objective response rates were 47% in metastatic disease and 48% in locally advanced disease. The new analysis adds follow-up time rather than claiming a different efficacy profile; the response rates are broadly similar, while complete responses have increased as patients have been tracked longer.
The safety profile
The safety findings are the other half of the story. The company reports few high-grade immune-related adverse events — 2.9% grade 3, with no grade 4 events and none leading to death — a profile it says stayed stable with longer follow-up. Immune-related adverse events define this drug class and can become serious, making a low rate of high-grade events a meaningful finding for a treatment that patients with cutaneous squamous cell carcinoma receive until their disease progresses.
Cosibelimab’s mechanism is the company’s explanation. It is a PD-L1-blocking antibody that also induces antibody-dependent cell-mediated cytotoxicity, and Sun Pharma emphasises that it preserves PD-L2 signalling, which may help maintain immune tolerance in non-tumour tissue. That is a plausible rationale for the tolerability profile, though it is a mechanistic argument rather than a proven clinical advantage. Like all drugs in this class, UNLOXCYT can cause severe or fatal immune-mediated reactions affecting multiple organ systems, so clinicians administer it under medical supervision.
What to watch
Three things will show whether the data translate into practice. First, peer-reviewed publication of the full results, since the current readout is a congress abstract. Second, whether head-to-head or real-world evidence emerges against the PD-1 inhibitors that already treat this disease — without it, the safety and mechanism arguments remain suggestive. Third, whether Sun Pharma expands access outside the United States, which it says it is pursuing, since availability shapes how many patients the data can help.
What the data do and don’t establish
They establish durable responses and a low high-grade irAE rate in a follow-up analysis of an approved drug for cutaneous squamous cell carcinoma, across 205 patients. They do not establish superiority to other checkpoint inhibitors, since the trial is single-arm and open-label with no comparator, or that the mechanism produces a clinical advantage. The cohorts are also modest in size, ranging from 63 to 78 patients.
The honest summary: This update shows that an already-approved oncology drug continues to deliver durable responses. Sustained responses, rising complete-response rates, and a low rate of high-grade toxicity make these findings genuinely encouraging for patients with difficult-to-treat skin cancer. The caveats are the familiar ones for single-arm oncology data — no comparator, small cohorts, company-reported figures — and the mechanism story, while plausible, awaits head-to-head evidence. As with any treatment decision, patients should discuss the risks and benefits with their clinician.
Editor’s Note: This article draws on the Sun Pharma release and the FDA‘s approval record and prescribing information for cosibelimab-ipdl, plus the ClinicalTrials.gov record for Study CK-301-101. The long-term efficacy and safety figures are as reported by the company from its ESMO 2026 abstract and are not independently verified; the trial is single-arm and open-label. This article is not medical advice; readers should consult a qualified clinician and the full prescribing information.