Xencor Shares Rise 24% After Selecting Proposed Phase 3 Dose of XmAb819
Key Facts
Xencor shares rose 24% on Monday, October 26, after the company presented updated Phase 1 data for its experimental drug XmAb819 for advanced clear cell renal cell carcinoma. The company published its results on October 25 and presented them at the ESMO 2026 conference in Madrid, according to its statement. Xencor selected an intravenous dose of 400 micrograms/kg as the proposed Phase 3 dose. In an analysis dated October 1, 5 of 11 patients evaluable for efficacy had a confirmed partial response, for a response rate of 45.5%. Investing.com coverage attributed to Reuters said the shares jumped after the dose-selection data were presented.
The results included one additional patient with an unconfirmed partial response, bringing the response rate to 55% when included, according to Xencor's statement. The confirmed rate is based on a small group of 11 patients who received the proposed dose, making it an early signal in a Phase 1 study. The company estimated six-month progression-free survival at 82% in the same group. Median progression-free survival had not been reached at the time of the analysis, while more than 70% of patients remained on treatment. These indicators provide a picture of the drug's clinical activity, alongside the response rate, before the dose is tested in a larger study.
The Phase 1 study enrolled 119 patients with advanced clear cell renal cell carcinoma and covered 11 intravenous dose levels through September 1, 2026. The expansion cohorts included 68 patients, whose median number of prior lines of therapy was three, according to company data. All patients had received at least one PD-(L)1 inhibitor and at least one VEGFR TKI. This background puts the results from the selected-dose group in the context of patients who had previously received multiple treatments. It also shows that the study collected data across different dose levels before identifying a proposed dose for later development stages.
The results come with safety signals that warrant attention in assessing the treatment. In the expansion cohort, 72.1% of patients experienced a treatment-related adverse event of Grade 3 or higher, while 5.9% discontinued treatment because of a related adverse event, according to Xencor's disclosure to the U.S. Securities and Exchange Commission. Grade 3 or higher AST elevation was the most common, at 35.3%, followed by ALT elevation at 33.8% and rash at 22.1%. The company said adverse events occurred mainly during the priming-dose period. It added that most severe liver enzyme elevations were transient and asymptomatic.
Xencor plans to start a global randomized study comparing XmAb819 with tivozanib as a control treatment. The company said that, if successful and after additional interactions with the U.S. Food and Drug Administration, the study could serve as the basis for an application for full approval. The company is targeting the start of a potential registration-supporting study by the end of 2027. It also expects data from at least 20 patients evaluable for efficacy at a dose of 400 micrograms/kg during the first half of 2027 to support dose selection. Xencor said in August that it was targeting the start of a registration-enabling study of the drug as a monotherapy during 2027.
The company is also escalating the subcutaneous dose in patients with advanced clear cell renal cell carcinoma, with results expected during the first half of 2027. This pathway adds another mode of administration to the XmAb819 program, while selection of the current intravenous dose remains central to planning the randomized study. The next regulatory steps are tied to additional interactions with the U.S. Food and Drug Administration. Whether the randomized study can support an application for full approval depends on its success. The next dated research milestone announced by the company is the availability of an efficacy cohort of at least 20 patients in the first half of 2027.