Cancer researchers just found a new way to take on tumors.

CAR T cell therapy revolutionized blood cancer treatment by supercharging a patient’s own immune cells to hunt down cancers. But the approach has struggled in solid cancers. These are some of our top killers—breast, lung, prostate. Roughly two million Americans are expected to be diagnosed with cancer in 2026, and over 600,000 will likely succumb to the disease.

Unlike blood cancers, solid tumors rarely share a single, universal target for CAR T cells. Even cells within the same tumor are a mishmash. Some have little or none of a target protein, allowing them to evade the engineered immune cells, survive treatment, and fuel relapse.

“Target discovery remains a considerable challenge in the development and translation of

CAR T cell therapies for solid tumors,” wrote Christopher Mount and Marcela Maus at the Massachusetts General Brigham Cancer Institute.

Now, two independent teams have converged on the same promising target: A cell-surface protein called GPNMB. In one study, CAR T cells engineered to recognize GPNMB rapidly destroyed glioblastoma—a lethal brain cancer—in tissues taken from patients and shrank tumors in mice.

A second team used a similar strategy against an aggressive soft tissue cancer to fight tumors in organoids and mice. In an early clinical trial involving a single participant, one infusion stabilized the disease for three months without serious side effects.

CAR T designers are often wary of broadly shared targets because they can trigger dangerous attacks on healthy tissue. But GPNMB is an odd duck. In addition to cancer cells, it also sits on immune cells that spur cancer growth or suppress the body’s innate ability to get rid of tumors.

“Our approach attacks both the tumor and the environment that allows it to thrive,” said Sheila Singh at McMaster, who led the glioblastoma study, in a press release. “We’re going beyond targeting the cancer alone and eliminating the immune cells that help shield it from treatment.”

Cancer Fortress

Solid cancers have plenty of tricks to outsmart CAR T cells.

Researchers make these supercharged immune cells  by extracting a patient’s own T cells and genetically engineering them to produce protein “claws” that latch onto a specific cancer target. After infusing the cells back into the body, they seek and destroy tumor cells. CAR T has transformed treatment for several blood cancers and is showing promise in autoimmune diseases and excessive heart and kidney scarring. To simplify the procedure, researchers are also exploring ways to directly transform T cells inside the body with gene therapy.

Solid cancers, however, are far tougher opponents. Unlike blood cancers, which are heavily coated with a shared target called an antigen, solid tumors are molecular patchworks. Cells within the same tumor can display different targets—or none at all—allowing some to evade a CAR T attack and trigger relapse. Many of these targets also appear on healthy tissues, raising the risk of dangerous side effects. And then there’s the tumor microenvironment: A toxic, glue-like “fortress” that hijacks immune cells and uses them to battle incoming CAR T cells.

These barriers aren’t impenetrable. Previous work enlisted  bacteria to help CAR T cells burrow into tumors. Other efforts engineered ultra-sensitive CAR T cells capable of detecting tiny amounts of a cancer target shared across multiple solid tumors.

“Recent reports of activity in several clinical trials reinforce optimism that these efforts may result in true clinical benefit,” wrote Mount and Maus, who were not involved in either study.

But these strategies require additional engineering steps, increasing complexity and cost. And most still leave one major roadblock intact: The tumor’s immune defenses.

One-Two Punch

In the glioblastoma study, the team at McMaster University scoured donated tumors for proteins that distinguished the most aggressive cancer cells. They found one standout: GPNMB. Another test of every protein dotting the cell surface confirmed it as a promising target. The protein is evident across a cancer cell’s membrane, making it readily accessible to CAR T cells.

In lab tests, CAR T cells engineered against GPNMB performed well, nearly eliminating tumors grown from patient samples and extending survival in mice.

The target turned out to be far more valuable than expected. The team soon realized that GPNMB also marked the immune cells that suppress anti-cancer drugs. CAR T cells attacked both fronts simultaneously, weakening the tumor’s immune shield and killing the cancer itself.

“Most approaches have focused on killing cancer cells alone,” said study author Shan Grewal. “Our work suggests we may also need to dismantle the immune support system that helps the tumor survive.”

The second team focused on alveolar soft-part sarcoma, a rare soft-tissue cancer that often spreads to the lungs, brain, and bones before it’s diagnosed. Treatment often comes too late.

The disease is driven by a type of “fusion” gene created when pieces of genetic material are accidentally stitched together. These genes are extremely tough to target directly. Instead, the team screened all surface proteins on the cancer cells and again landed on GPNMB as a top candidate for intervention. The protein’s levels closely tracked the activity of the fusion gene.

CAR T cells targeting GPNMB cleared tumors and prevented metastasis in mice. But because an earlier antibody drug against the protein caused severe skin toxicity in patients, the team also tested their CAR T cells in mice carrying small human skin grafts. Although inflammation initially flared, there were no signs of ongoing skin damage.

Encouraged, the team treated a patient with relapsed, metastasized alveolar soft-part sarcoma. After a single infusion, the engineered cells rapidly divided in the bloodstream and remained detectable for roughly a month. The treatment didn’t trigger skin rashes or more dangerous side effects, like cytokine release syndrome where the body mounts a hyperactive immune defense that harms healthy organs.

The treatment’s benefits outlasted the engineered cells themselves. For roughly three months, imaging tests found fewer of the small, round spots on the patient’s lungs that often signal metastatic cancer, suggesting the disease had stabilized.

A final analysis identified another roadblock: Clusters of cells that suppress the immune system and could blunt the benefits. Adding drugs to block these immune molecules boosted tumor killing in mice. Because the same kind of gene fusion drives other cancers, including kidney, the CAR T cells could have reach beyond this specific type of sarcoma.

Together, the studies underscore that the best CAR T targets might extend beyond cancer cells to expose and attack cancer’s immune cell supporters too. Finding a viable target is a delicate balancing act. Chosen well, and CAR T cells could tackle multiple drivers for cancer growth. Choose poorly, and healthy tissues could get hurt in the crossfire.

Even so, “these two studies indicate that GPNMB represents an actionable target for CAR T cell therapies in several solid tumors,” wrote Mount and Maus.