Xencor Stock Catapults 25% to a Near Four-Year High After 'Unprecedented' Kidney Cancer Data

Xencor Stock Jumped More Than 25% on Monday — Here Is the Short Answer

Xencor (NASDAQ: XNCR) stock catapulted more than 25% on Monday, October 26, 2026, briefly hitting its highest level since February 2023, after the Pasadena-based biotech reported Phase 1 results for its experimental kidney cancer drug XmAb819. At the dose Xencor has now selected for Phase 3, 45.5% of evaluable patients with advanced clear-cell renal cell carcinoma saw their tumours shrink — a result one William Blair analyst called "unprecedented" and "profound." Xencor closed Friday at $25.18, traded as high as $33.60 on Monday, and was the second-biggest premarket gainer in the entire U.S. market, up 32.68% before the bell.

What Happened

Xencor released the Phase 1 dose-expansion results on Sunday, October 25, ahead of a presentation at the ESMO oncology congress and a company webcast on Monday morning at 7:00 a.m. EDT. The trial tested XmAb819 in heavily pretreated patients with advanced clear-cell kidney cancer — people who had already received a median of three prior lines of therapy, and who had all previously been treated with both a checkpoint inhibitor and a VEGF-receptor tyrosine kinase inhibitor.

At the selected dose of 400 micrograms per kilogram given intravenously, five of 11 evaluable patients had confirmed tumour shrinkage, for a confirmed response rate of 45.5%. Lower doses also produced responses: 30% at 100 micrograms per kilogram among 30 evaluable patients, and 44% at 200 micrograms per kilogram among 25 evaluable patients. Across the study, nearly 86% of patients were deemed to have their disease under control, and the six-month progression-free survival estimate at the selected dose was 82%, with median progression-free survival not yet reached at the September 1 data cutoff.

Why It Is Blowing Up

The bar for success was much lower than the result. Wedbush analyst David Nierengarten said Xencor only needed a 25% objective response rate to succeed, and he raised his price target to $45 from $30 after the data. William Blair analyst Matt Phipps said the conference discussant summed it up in calling the result "only the floor" for XmAb819, because patients were so heavily pretreated and results could improve in earlier lines or combinations. Phipps said the profile gives the drug "blockbuster potential" in kidney cancer.

XmAb819 is a T-cell engager — an engineered antibody designed to connect ENPP3-expressing tumour cells with CD3-bearing immune T cells so the immune system can destroy the cancer cells. That mechanism, plus a response rate roughly double the 22% Merck's Welireg posted in its randomized later-line trial, is why traders piled in.

Key Facts

Stock move: XNCR rose more than 24% in early trading to $31.35 and was up about 25.3% at $31.56 intraday, from a $25.18 Friday close; premarket it gained 32.68% to $33.37, the second-largest premarket gain in the U.S. market.
Response rate: 45.5% confirmed responses at the selected 400 mcg/kg dose (5 of 11 evaluable patients); 45% at the highest dose in the broader read reported by Investor's Business Daily.
Disease control: Nearly 86% of the 42 previously treated patients highlighted in the main cohort had disease under control.
Selected dose: 400 micrograms per kilogram intravenously is now the proposed Phase 3 dose.
Next regulatory step: Xencor plans FDA discussions in the first half of 2027 about a potential accelerated approval pathway in selected patient subgroups, and plans to initiate a potential registration-enabling study next year, including a global randomized study of XmAb819 alone versus tivozanib.
Cash position: Management says its cash runway extends into 2029.
Safety caveat: Severe or worse treatment-related adverse events occurred in 72.1% of patients across the combined dose-expansion cohorts, including liver-enzyme elevations, rash, low blood pressure and cytokine release syndrome; treatment-related events caused discontinuation in 5.9% of patients. The cohorts were small and uncontrolled, with no control arm.

What Is Next

The honest takeaway is that this is promising early data, not proof. The selected-dose cohort was just 11 evaluable patients, the 95% confidence interval on the 45.5% response rate runs from 16.8% to 76.6%, and without randomization the results cannot establish superiority over existing treatments. What happens next will decide whether Monday's breakout holds: the planned registration-enabling study, FDA discussions in early 2027, and whether responses hold up in earlier treatment lines and combinations. This post reports what happened and why markets reacted; it is not financial advice.

Sources

FAQ

Why did Xencor stock jump on October 26, 2026?

Xencor reported Phase 1 results for XmAb819 showing a 45.5% confirmed response rate at its selected dose in advanced kidney cancer, well above the 25% rate analysts said it needed, sending the stock up more than 25% to a nearly four-year high.

What is XmAb819?

XmAb819 is Xencor's experimental T-cell engager antibody. It connects ENPP3-expressing kidney tumour cells with CD3-bearing immune T cells so the immune system can destroy the cancer cells.

What dose did Xencor pick for Phase 3?

Xencor selected 400 micrograms per kilogram given intravenously as the proposed Phase 3 dose, after five of 11 evaluable patients at that dose had confirmed tumour shrinkage.

When could XmAb819 reach the market?

There is no approval date yet. Xencor plans FDA discussions in the first half of 2027 about a possible accelerated approval pathway and intends to start a registration-enabling study next year, so any approval would depend on those steps succeeding.