STAT3 sustains tumorigenicity following mutant KRAS ablation.

Oncogenic KRAS mutations underlie some of the deadliest human cancers. Genetic or pharmacological KRAS inactivation produces mixed outcomes and frequent relapse. Mechanisms of tumor resistance to KRAS inhibition remain poorly understood. We present evidence that STAT3 supports tumor growth following KRAS depletion. Using a conceptual framework of pancreatic ductal adenocarcinoma, we show that cancer cells that survive CRISPR-mediated ablation of mutant KRAS are dependent on STAT3 function to maintain tumorigenicity. Mechanistically, the combined loss of mutant KRAS and STAT3 disrupts a core transcriptional program of cancer cells critical to oncogenic competence. This in turn impairs tumor growth in mice and enhances immune rejection, leading to tumor clearance. We propose that the STAT3 transcriptional program operating in cancer cells enforces their malignant identity, rather than providing classical features of transformation, and shapes cancer persistence following KRAS inactivation. Our findings establish STAT3 as a critical enforcer of oncogenic identity in KRAS-ablated tumors, revealing a key vulnerability.