Xencor shares jump 24% after XmAb819 data point to proposed Phase 3 dose
Key Facts
Xencor shares jumped 24% on Monday, October 26, after the company presented dose-selection data for XmAb819, according to Investing.com. The company announced updated results on October 25 from a Phase 1 study in patients with advanced clear cell renal cell carcinoma. The data were presented at the European Society for Medical Oncology 2026 Congress in Madrid. Xencor selected an intravenous dose of 400 micrograms per kilogram as the proposed Phase 3 dose. The program remains in development, however, and the reported data relate to an early-stage study and dose selection, not definitive proof of the treatment's efficacy.
In the selected-dose group, the efficacy-evaluable population included 11 patients as of the October 1, 2026, data cutoff. Five confirmed partial responses were recorded, equivalent to a confirmed objective response rate of 45.5%, along with one unconfirmed partial response that raised the unconfirmed rate to 55%. The company estimated six-month progression-free survival at 82% using the Kaplan–Meier method. Median progression-free survival in this group had not been reached, while more than 70% of patients remained on treatment. The company said these results supported selecting a dose of 400 micrograms per kilogram for the next stage.
Company data show limited variation in confirmed response rates among the higher doses presented. The rate was 30% at 100 micrograms per kilogram, rose to 44% at 200 micrograms per kilogram, then to 45.5% at 400 micrograms per kilogram. In the dose-expansion cohorts, the median number of prior lines of therapy was three, and 94% of patients were classified as intermediate or high risk. The company says all patients in those cohorts had previously received at least one PD-(L)1 inhibitor and at least one VEGFR TKI inhibitor. In addition, 63% had previously received two or more VEGFR TKI inhibitors, and 34% had received at least one HIF2α inhibitor.
Across the broader study, Phase 1 included 119 patients across 11 targeted intravenous dose levels as of the September 1, 2026, data cutoff. The dose-expansion cohorts included 68 patients, while the selected-dose results reflect a smaller group of 11 patients. Among 25 patients who achieved a confirmed response under RECIST v1.1 criteria, one complete response and 24 partial responses were recorded. Nineteen responses were ongoing at the data cutoff, and median treatment duration was seven months. Investigator Sumanta Pal said available treatments include checkpoint inhibitors and therapies targeting the VEGF axis, and described XmAb819's proposed mechanism as "completely different."
Safety data stand alongside response indicators in the combined dose-expansion cohorts. A total of 5.9% of patients discontinued treatment because of treatment-related adverse events, while treatment-related adverse events of Grade 3 or higher were recorded in 72.1%. The most notable of these events included elevated AST at 35.3%, elevated ALT at 33.8% and rash at 22.1%. Xencor plans to conduct a global randomized trial comparing XmAb819 with tivozanib in patients previously treated with a PD-(L)1 inhibitor and at least one VEGFR TKI inhibitor. The company said that, if successful and following further discussions with the U.S. Food and Drug Administration, the study could form the basis for full approval.
The company plans to discuss a potential accelerated approval pathway with the U.S. Food and Drug Administration for specific groups of patients with clear cell renal cell carcinoma during the first half of 2027. It also expects at least 20 efficacy-evaluable patients at the 400 micrograms per kilogram dose to be available to support dose selection during the same period. Alongside the main program, a sub-study of advanced ENPP3-positive tumors began enrollment in the second quarter of 2026, including colorectal cancer, non-small cell lung cancer and papillary renal cell carcinoma. Another sub-study in patients with advanced renal cell carcinoma began enrollment in the third quarter of 2026. Xencor said its liquidity would fund operations through 2029, while cash, cash equivalents and marketable securities totaled $486.4 million on June 30, 2026, compared with $610.8 million on December 31, 2025.