Genmab has shared the first data on rinatabart sesutecan (Rina-S) in advanced endometrial cancer. The biotech reported a 50% unconfirmed response rate, beating the expectations of William Blair analysts to boost confidence in the program ahead of its move into phase 3.
Rina-S is a FRα-directed ADC that Genmab picked up last year in its $1.8 billion takeover of ProfoundBio. At the time, Rina-S was in a phase 1/2 trial in ovarian cancer and Genmab outlined an opportunity worth $1 billion or more. Subsequently, the biotech identified a broader set of target indications and dialled up its valuation of the opportunity to $2 billion or more.
Endometrial cancer represents a meaningful piece of the opportunity, making the publication of the first clinical data in this setting a key early test of Genmab’s growing ambitions for the ADC. Rina-S passed the test.
Ahead of the American Society of Clinical Oncology (ASCO) Annual Meeting that begins next week, Genmab reported unconfirmed response rates of 50% and 45.5%, respectively, in the lower and higher dose cohorts. The biotech saw two complete responses at the lower dose. Around 80% of the responses were ongoing in both cohorts as of the cutoff. The patients had received one to eight lines of prior therapies before joining the trial.
Talking on an earnings call earlier this month, Tahamtan Ahmadi, chief medical officer at Genmab, said a combination of chemotherapy and checkpoint inhibition is the new frontline treatment for the tumor type. The evolution of the treatment pathway and lack of control arm in Genmab’s trial complicate efforts to contextualize the results but Ahmadi provided a historical basis for the biotech’s excitement.
“Historically, the second-line has been an indication where the response rate to chemotherapies are maybe in the 10% to 15% range,” Ahmadi said. “We feel very comfortable that the data that is going to be presented in the very near future and publicly available will underscore the point that this is really a best-in-class profile from an efficacy point of view as well as from a durability point of view.”
William Blair analysts said a response rate of 30% or more would generate confidence in the program. With Genmab clearing that bar and reporting no ocular toxicity, neuropathy or interstitial lung disease, the analysts have increased confidence in the phase 3 endometrial cancer trial that the biotech plans to start by the end of 2025.
Genmab sees endometrial cancer as a proving ground for the idea that Rina-S can be effective across the spectrum of folate receptor alpha expression. Broad effectiveness forms part of Genmab’s argument that Rina-S can improve on AbbVie’s Elahere, an approved ADC against the same target. AbbVie has sued Genmab over Rina-S, accusing the biotech of being “willfully blind” to the theft of trade secrets.