Recruiting in Pennsylvania · September 29, 2026
Penn Vet opens a CAR-T study for dogs with histiocytic sarcoma
Penn Vet is conducting a pilot CAR-T study for dogs with histiocytic sarcoma (HS). On September 29, investigator Matthew Atherton confirmed to Vet Trial Finder that enrollment is open, although places are limited.
The team collects T cells from the dog's own blood and engineers them to recognize STEAP1, a protein found on the surface of some tumor cells. The cells are then infused back into the dog with the aim of attacking the cancer. Penn can test stored tumor tissue for STEAP1 first; a tumor without that target would not qualify. The prior consent form also includes two doses of bendamustine before the CAR-T infusion.
The idea is interesting, but this is the first time this CAR-T approach is being tested in dogs with HS. The pilot is primarily establishing safety and an appropriate dose. There are no published results showing how often it shrinks canine HS or extends survival. A measurable tumor is required for enrollment. A dog with no detectable tumor after surgery does not qualify under the current protocol.
Among current HS studies, the Phase II trametinib trial at the University of Florida and other sites has a stronger foundation of preliminary disease-specific evidence. Trametinib interrupts a growth-signaling pathway inside cells. It inhibited canine HS cells in laboratory and mouse-model work and was subsequently studied for tolerability in dogs with different cancers. The Phase II study is now testing whether it actually shrinks HS in dogs. Those results are not yet available, and no validated test can reliably predict which dog will respond.
The distinction is how the treatments are intended to work: trametinib tries to interrupt growth signals within tumor cells, while CAR-T aims to direct immune cells to recognize and kill them. Both could theoretically shrink an existing tumor; neither has yet demonstrated a clinical benefit in dogs with HS. Trametinib has more preliminary evidence specific to this disease. CAR-T could become a powerful approach, but we do not yet know whether it will work in HS or for how many dogs.
Previous cancer treatment does not automatically rule out participation at Penn, but concurrent chemotherapy is not allowed. According to a previously issued consent form, the study covers protocol-specified testing and treatment, while coverage for complications directly caused by study treatment is limited to $1,000. Penn is revising the form, so owners should confirm the current schedule, eligibility and costs before enrollment.
Study details and investigator contact are on the Atherton Laboratory's official page: mattath@upenn.edu. To review trials that may fit a particular dog, use Vet Trial Finder's free HS search. A search result is only a starting point; the study team makes the final eligibility decision.