GSK's Ris-Rez Data Lift the Opportunity, Not the Certainty

GSK's experimental cancer drug risvutatug rezetecan, known as Ris-Rez, produced a stronger response rate at the higher dose in a small global study. Eleven of 18 evaluable patients responded at 8 milligrams per kilogram, a 61% objective response rate, compared with seven of 22 patients, or 32%, at 6 milligrams per kilogram.

The result helps explain Jefferies' Buy rating and 2,500 pence price target, which implied about 34% upside in the source report. The bank estimated peak sales of roughly $3 billion. Those figures are analyst estimates, not company guidance, and the clinical evidence is still early.

GSK's presentation also cited response rates of 52.3% and 58.3% in two Chinese studies. A rival program from Merck reported 48.2% in a separate trial. Those numbers were generated in different studies with different patients and protocols, so they should not be read as a head-to-head comparison.

Safety and durability now matter more than a single response rate. Treatment-related adverse events occurred in 42% of the 50 patients in the global study, including one case of interstitial lung disease. Progression-free survival data were not mature enough to establish how long responses last.

The trial suggests the higher dose may have more activity, but the sample is too small to settle the risk-benefit profile. Investors should watch for larger cohorts, duration of response, progression-free survival and whether lung toxicity changes with exposure. Those data will determine whether the early efficacy can support the multibillion-dollar sales expectations embedded in bullish analyst models.