A new cancer pill may help the immune system see tumors that once stayed hidden

Many cancer patients initially respond well to immunotherapy, only to see their tumors return months or years later.

Cancer cells often evolve ways to avoid immune attack, leaving doctors with fewer treatment options once the disease begins growing again.

Researchers have long suspected that one of those escape routes involves a molecular system that tumors use to hide from immune cells.

A new pill designed to block that mechanism has now shown its first signs of success in patients.

Tumors stay hidden

Cancer cells survive by staying out of sight. Many dial down the molecular name tags on their surface that immune cells normally read, so the patrol glides past without noticing anything wrong.

One trick behind that vanishing act runs through an enzyme called ERAP1, which trims the protein fragments a cell shows as identification.

Tumors tune it to erase the fragments that would flag them as a threat, a dodge a broad review has mapped.

Professor Fiona Thistlethwaite, a consultant medical oncologist at the Christie NHS Foundation Trust, led an international trial built around stripping that disguise away.

The plan was to expose hidden tumors, then let an existing immune drug finish the job.

Purpose of the pill

The trial centered on GRWD5769, a pill developed by the Oxford biotech firm Greywolf Therapeutics.

It blocks ERAP1 so the enzyme can no longer wipe those identifying fragments off a tumor’s surface.

With the disguise stripped away, the idea is that T cells can finally spot tumors they had been missing.

That would clear the way for cemiplimab, an immunotherapy already on the market, to lock on and attack. Patients take the pill on an on-and-off schedule rather than every day.

The design aims to keep presenting the immune system with fresh targets. In theory, this could stop immune cells from wearing out.

Testing it in people

The trial, called EMITT-1, enrolled 83 patients across 28 centers in four countries.

Everyone had advanced cancer and had exhausted most treatment options. Six common cancers were covered – lung, bladder, liver, bowel, cervical, and head and neck.

In most of these patients, immunotherapy had already failed, the sort of dead end where research shows only a fraction still benefit.

Alongside GRWD5769, each person received the immunotherapy cemiplimab, the drug meant to do the attacking once tumors were exposed.

Details from the scans

Tumors shrank in 26 of the 83 patients, and in 15 patients by at least 30 percent. This showed significant retreat for cancers that had kept growing despite everything thrown at them.

The length of the responses was telling. The treatment held the disease in check for six months in nearly a fifth of cervical cases, a third of liver and bladder cases, and over half of bowel and lung cases.

What caught the researchers’ attention was the pattern across so many tumor types at once, not one standout result.

“That’s unusual at such an early stage, when we’re usually just looking at how safe it is,” said Thistlethwaite.

A long-held idea

Scientists had suspected for years that blocking ERAP1 might wake the immune system back up.

Lab dishes and animal studies hinted that switching off the enzyme could leave stubborn tumors open to attack.

Until this trial, no one had shown the idea working inside actual patients. It had certainly not been shown in people whose cancer had already shrugged off immunotherapy.

That gap between a promising theory and clinical success is where most cancer ideas quietly die.

These were people with few choices left, and many stayed on the pill for months without their cancer advancing.

For a group expected to keep getting worse, holding steady counts as a major win.

Easy on patients

A new cancer drug usually comes with a price in side effects. This one mostly did not produce serious side effects.

The side effects patients reported were mild, and nothing serious enough to stop treatment turned up.

Because it is a capsule rather than an infusion, GRWD5769 also fits more easily into daily life. Patients take it at home, which helps explain why many stayed on it long enough to benefit.

Tolerability like that opens up options. Its mild side-effect profile makes it easy to pair with other treatments. The team is keen to test it in new combinations without piling on harm.

Results filled with hope

What the trial established is concrete. Blocking ERAP1 with a pill can pull the disguise off tumors in patients and revive an immune attack that had stalled.

If larger trials hold up, doctors could gain a way to rescue immunotherapy after it stops working, instead of watching it slip away with nothing left to try.

That possibility reaches a huge number of patients who hit that wall today. Greywolf is already preparing a larger, randomized study involving broader patient groups.

The deeper change, though, is in the thinking. For the first time, researchers have successfully removed a disguise they long suspected tumors were using in human patients.

The study is published in the Journal of Clinical Oncology.

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