Early trial: a new immunotherapy drug shrank some tumors that usually resist it

If you or someone you love has faced cancer, you have probably heard the word immunotherapy. It helps many people, but not everyone. A new early trial shows a different way to switch on the immune system, and it shrank tumors in some people whose cancers had ignored other immune treatments.

The drug is called invikafusp alfa. It is still being tested, so it is not something you can ask for at the pharmacy. What this trial gives you is a clearer picture of where cancer research is heading, and a reason to know the right question to ask if cancer ever touches your family.

How the study worked

START-001 is a phase 1/2 trial published on Oct. 23, 2026, in Nature Medicine. In phase 1, 34 people with solid tumors, most of them with cancers that had already resisted standard immunotherapy, received rising doses to find a safe and useful one, and 18 more joined the first part of phase 2; because this kind of early trial has no comparison group and is built mainly to test safety and dose, it cannot yet say how well the drug works overall.

What they found

The drug is a lab-made antibody that activates two specific groups of T cells, which are immune cells that can attack tumors. Here is what happened.

• Tumors shrank in some people. At the two best doses, 0.08 and 0.12 milligrams per kilogram of body weight, the overall response rate was 14.8%. That is 4 of 27 people, or roughly 15%, whose tumors shrank.
• Some of those tumors were the hard kind. The responses included microsatellite stable colorectal cancer and lung cancer that was PD-L1-negative. Both usually respond poorly to immunotherapy.
• Dose mattered. No tumors shrank at doses lower than 0.08 mg per kilogram.
• The drug did what it was designed to do. It increased the targeted T cells in the blood and inside tumors, with the biggest rise at the best doses.
• Side effects were mostly mild to moderate. The most common one was cytokine release syndrome, an immune reaction that can cause fever and other symptoms. Two people had serious side effects that went away, and there were no treatment-related deaths.
• No upper limit was reached. Even at the highest dose tested, 0.16 mg per kilogram, researchers did not hit the maximum dose the body could tolerate.

Based on all of this, the team picked 0.08 mg per kilogram as the dose to carry into the next stage of testing. That stage is still underway, and it is meant to show which cancer types respond best.

What is a “cold” tumor?

Immunotherapy often works by releasing the brakes on the immune system. That helps when a tumor already has plenty of immune cells inside it. A “cold” tumor has very few of them, so releasing the brakes does little.

Invikafusp alfa works differently. Instead of releasing brakes, it presses the accelerator on two specific groups of T cells. That is why the responses in cold tumors are the part researchers find most interesting.

One way to read this trial: it does not give you a new treatment today, but it adds a new idea to the toolbox. Many drugs that are now routine began with early results like these.

What you can do today

If you or someone close to you has an advanced cancer that stopped responding to treatment, write down one question for the next oncology visit: “Are there clinical trials, including early ones, that might fit my situation?” Then take a few minutes to look at ClinicalTrials.gov, the free US government registry, where this trial is listed under the number NCT05592626. Seeing how trials are described there makes the conversation with your care team easier.