Cell Surface Flag Identified as Potential Cancer Target

By Curie | Biotech Reporter

March 13, 2026 — For five decades, scientists have known about Src, a notorious cancer-causing enzyme that was the first oncogene ever discovered, earning its discoverers a Nobel Prize in 1989. But it was always assumed to live inside cells, hidden from the immune system. Now, researchers at UCSF have found it exposed on the outside of tumor cells — like a red flag marking them for destruction.

In a study published in Science, the team discovered that Src appears on the surface of bladder, colorectal, breast, pancreatic, and probably many other tumor cells. The enzyme gets pushed outside through the cell's waste disposal system, which becomes overloaded in fast-growing cancer cells.

"No one thought to look for it on the outside," said Jim Wells, PhD, professor of pharmaceutical chemistry at UCSF and senior author of the study. "Our discovery enables us to test proven immunotherapies on this new tumor target."

The key insight: while drugs that target Src inside cells have struggled because they affect healthy cells too, targeting the extracellular version (eSrc) could allow antibodies to specifically hunt cancer cells. The researchers showed that antibodies carrying radioactive payloads or summoning immune cells killed cancer cells and shrank tumors in mice.

"This is truly exciting," said Corleone S. Delaveris, PhD, first author of the paper, now at Inversion Therapeutics. "We saw that SRC was getting swept out onto the outer membrane, where it sat exposed like a red flag."

The team found eSrc on tumor cells from patients but not on healthy tissue, suggesting it could be specific enough to guide cancer-killing antibodies without harming normal cells. The researchers estimate the target could apply to up to half of all tumors.

UCSF has licensed the antibodies to Inversion Therapeutics to explore their therapeutic potential.