BLOCKADE OF TUMOR-INTRINSIC TGF-Β SIGNALING DRIVES HYPERPROGRESSION IN SMALL CELL LUNG CANCER

Stromal immunosuppressive pathways are key modulators of response to immune checkpoint inhibitors, but their tumor-intrinsic consequences remain incompletely defined. We conducted a clinical trial of bintrafusp alfa, a bifunctional PD-L1/TGF-β inhibitor, in small cell lung cancer. Among 34 evaluable patients, 18% had partial responses, 20% stable disease, and 62% progressive disease; 38% of progressors met criteria for hyperprogressive disease (HPD). HPD was also observed across other tumor types (n=450), in higher frequencies with bintrafusp than PD-(L)1 blockade alone. Blood and tumor profiling showed that HPD correlated with systemic immune suppression and elevated TGF-β signaling. Functional studies demonstrated that tumor-intrinsic TGF-β signaling restrains proliferation in a subset of SCLC; pathway blockade triggers hyperproliferation. External validation across cell lines and tumor samples confirmed a tumor-intrinsic TGF-β-high transcriptional state associated with inferior survival. Together, these findings identify a context-dependent, growth-constraining function of TGF-β and support tumor-intrinsic biomarker-guidance while targeting stromal immunosuppressive pathways.