Alpha Tau’s Cancer Combination Just Delivered a Response Rate More Than 5X Keytruda’s Historical Benchmark

WSW, NY, July 29th, 2026, FinanceWire

Pembrolizumab is the world's best-selling cancer drug at $31.7 billion in 2025 revenue, but in head and neck cancer it has a limitation: used alone, it produces tumor responses in only about one in five patients. Conventional radiation, which might help, tends to destroy the immune cells the drug depends on. Alpha Tau Medical Ltd. (Nasdaq: DRTS) set out to test whether a different kind of radiation could change that equation.

On July 21, the company presented data suggesting it may have. In a podium presentation at the AHNS 12th International Conference on Head and Neck Cancer in Boston, the company reported that every evaluable patient in a prospective study combining Alpha DaRT with pembrolizumab responded to treatment, with median overall survival nearly 50% longer than what pembrolizumab has achieved on its own.

What the study tested

The trial, conducted at Hadassah University Medical Center, enrolled elderly patients with locally advanced or metastatic head and neck squamous cell carcinoma whose tumors tested positive for PD-L1, a protein that helps predict whether a patient may respond to immunotherapy. That is the same population eligible for first-line pembrolizumab under the standard of care established by KEYNOTE-048, the pivotal trial that made Keytruda the default treatment in this setting. Each patient received a lead-in dose of pembrolizumab, followed by Alpha DaRT sources inserted directly into a tumor. The sources were removed approximately two weeks later, and patients continued pembrolizumab per standard dosing.

Eleven patients were enrolled. Two died before tumor response could be evaluated: one before receiving Alpha DaRT treatment, and one shortly after from what the company described as an unrelated cardiovascular event. That left nine patients evaluable for response. The mean age was 72, with the oldest patient 96.

The numbers

Among the nine evaluable patients, treatment produced a 100% objective response rate, meaning every patient's tumors measurably shrank or disappeared. Four achieved complete responses and five partial responses. By comparison, pembrolizumab alone in the same population produced a response rate of approximately 19% in the trial that established it as the standard of care.

Median overall survival was 18.2 months, compared with 12.3 months for pembrolizumab alone in a similar population. Median progression-free survival, the time before tumors began growing again, was 5.4 months versus approximately 3.2 months. Four patients remained alive at the time of analysis.

On safety, Alpha DaRT added almost nothing to the standard pembrolizumab regimen. No Alpha DaRT-related serious adverse events were observed. The only two Alpha DaRT-related adverse events across the treated cohort were Grade 1, the mildest classification.

Why these numbers matter

A 100% response rate against a 19% historical benchmark is not a marginal improvement, even in a nine-patient, single-center study without a randomized control group. The trial was designed to stop early if the results were clearly working or clearly not, and it stopped for success: the pre-specified threshold required more than six patients to respond, and all nine did. The comparisons to the pembrolizumab standard of care are historical rather than head-to-head, and larger controlled studies would be needed to confirm a survival benefit, but the size of the gap is what makes the signal worth noting, even with the caveats above.

What makes the combination hypothesis compelling is the mechanism. Conventional external-beam radiation can suppress the very immune cells it is supposed to activate. Alpha DaRT delivers high-energy alpha particles directly inside the tumor through tiny radium-224 sources, and the radioactive daughters diffuse only millimeters before decaying. The surrounding tissue, including immune cells, is largely spared. The theory has always been that this could prime an immune response rather than suppress one. The AHNS data suggest that theory may be translating into clinical outcomes.

Prof. Aron Popovtzer, Director of the Sharett Institute of Oncology at Hadassah and the study's lead investigator, said that "to my knowledge, no other combination study with pembrolizumab has shown results like these in this patient population."

What comes next

Alpha Tau said it is discussing a larger U.S. study of the Alpha DaRT-pembrolizumab combination with the FDA. A U.S. trial in this setting would be a step toward the kind of controlled evidence that could support a regulatory filing.

Keytruda is approved in more than 40 U.S. cancer indications. In any setting where the immune environment matters to treatment response, a radiation therapy designed to spare it could, in principle, be relevant. After years of preclinical evidence and monotherapy results across head and neck, skin, pancreatic, and brain cancers, the AHNS presentation is the first time Alpha Tau has shown that its combination thesis can produce survival data in patients receiving a checkpoint inhibitor. For the company's broader clinical strategy, that may prove to be among the most significant clinical results it has generated to date.

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