Ris-Rez improved OS against topotecan in relapsed SCLC in China

An eight-month difference in median overall survival, on a hazard ratio of 0.46

Patients randomised to risvutatug rezetecan lived a median of 18.5 months, against 10.3 months for those randomised to topotecan. The hazard ratio was 0.46, with a 95% confidence interval of 0.35 to 0.62 and a p-value below 0.0001, which GSK describes as a 54% reduction in the risk of death. The confidence interval sits well clear of 1.0 at both ends, so the direction of the result does not rest on the point estimate alone.

The comparison was made in 461 randomised patients, 230 on Ris-Rez and 231 on topotecan, at a median follow-up of 12.2 months. That follow-up is shorter than the median survival reported on the experimental arm, which means the 18.5-month figure is an estimate drawn from a curve that a substantial number of patients have not yet reached the end of. The announcement gives no landmark survival rate at 12 or 18 months, so how the two curves separate over time cannot be read from what has been released.

Patients were randomised 1:1 to risvutatug rezetecan at 8.0 mg/kg every three weeks or to topotecan at 1.2 mg/m² on days 1 to 5 of a 21-day cycle. Topotecan is the comparator because it is what second-line small cell lung cancer has had for many years. The trial was open-label, so patients and investigators knew which arm they were on, and overall survival is the endpoint least disturbed by that knowledge.

A 58.3% objective response rate where topotecan reached 12.6%

The objective response rate was 58.3% on Ris-Rez and 12.6% on topotecan, and the disease control rate was 90.4% against 60.2%. Median progression-free survival was 7.2 months against 3.0 months, with a hazard ratio of 0.33 and a 95% confidence interval of 0.25 to 0.42. The progression-free survival separation is proportionally larger than the overall survival separation, a pattern often seen when patients go on to further lines of therapy after progression.

The response and disease control figures were assessed by an independent review committee, which removes the main risk an open-label design carries for them. The announcement carries no duration of response, so how long the 58.3% of patients who responded held that response is not established by anything released so far, and it does not say whether progression-free survival was read by the same committee or by investigators.

Nor does the announcement separate limited-stage from extensive-stage disease, although the trial admitted both. Those two populations differ in prior treatment and in prognosis, and a reader deciding where this agent might sit would want the two apart. The full presentation may carry more than the announcement does.

Fewer grade 3 or higher treatment-related events on the antibody-drug conjugate arm

Treatment-related adverse events of grade 3 or higher were reported in 60.9% of patients on Ris-Rez and 78.2% of patients on topotecan. The most common on the Ris-Rez arm were decreased neutrophil count, decreased white blood cell count, anaemia, decreased lymphocyte count and decreased platelet count, so the toxicity that dominates on the Ris-Rez arm is haematological. The announcement lists no individual adverse events for the topotecan arm.

A grade 3 rate above 60% is a substantial toxicity burden in absolute terms, and the favourable comparison rests on topotecan performing worse still. The announcement reports no discontinuation rate, no dose reduction rate and no treatment-related death count for either arm, and it gives no figure for interstitial lung disease, which is the toxicity that has proved decisive for several antibody-drug conjugates in thoracic oncology. None of those absences is evidence of a problem, and none of them can be filled in from what has been released.

“Relapsed small cell lung cancer remains one of the most challenging cancers to treat, with few therapies delivering meaningful improvements in survival once the disease returns. In ARTEMIS-008, patients receiving Ris-Rez lived substantially longer while experiencing lower rates of severe treatment-related side effects. These findings suggest Ris-Rez could represent an important advance for patients.”Jie Wang, Chair of the Medical Oncology Department, National Cancer Center, Chinese Academy of Medical Sciences, and principal investigator of ARTEMIS-008

Enrolment was in China only, and the designations already granted rest on earlier evidence

ARTEMIS-008 recruited in China, and every patient contributing to these figures was treated there. Second-line practice, the platinum regimens given first line and the proportion of patients well enough to reach a second line all vary between health systems. A result established in one country therefore poses a question about the others, and GSK describes a global development programme for the agent in later-line and earlier settings that would have to answer it. The trial is Hansoh Pharmaceutical’s, and GSK holds rights to the agent outside mainland China, Hong Kong, Macau and Taiwan.

The agent already carries orphan drug designations for small cell lung cancer in the United States, Japan and the European Union, a breakthrough therapy designation in the United States for relapsed or refractory extensive-stage disease, and PRIME designation from the European Medicines Agency in the same setting. Those are procedural standings granted on earlier evidence and they commit no regulator to an approval. GSK’s announcement names no regulatory filing arising from ARTEMIS-008, and it does not describe this analysis as final.