Low-dose RT (9Gy) + pembrolizumab boosts early T-cell infiltration and trends to higher nodal clearance in node+ TNBC

TBCRC-053 (P-RAD; NCT04443348) tested adding preoperative breast-only radiation (0Gy vs 9Gy vs 24Gy) concurrently with pembrolizumab to a KEYNOTE-522–like neoadjuvant backbone (paclitaxel/carboplatin → AC, all with pembrolizumab) in node-positive TNBC (ER/PR<10%, HER2−); 55 enrolled, with 48 evaluable for the primary immunologic endpoint and 51 for ypN0. Upper-quartile 2-week tumor T-cell infiltration (multiplex IF “Immunoscore”) rose to 80% with 9Gy and 82% with 24Gy (vs 44% with 0Gy; p<0.0001 for both RT arms vs pretreatment reference), while nodal pCR (ypN0) was 73.3% (0Gy), 88.2% (9Gy), and 78.9% (24Gy); breast+node pCR (ypT0/TisN0) was 66.6%, 76.5%, and 68.4%, respectively (underpowered for between-arm testing). For external context, neoadjuvant pembrolizumab + chemotherapy in KEYNOTE-522 delivered ~64.8% pCR (ypT0/Tis ypN0) overall (vs 51.2% with chemo alone), so the pCR range here (≈67–77%) looks directionally in-family with pembrolizumab-based SOC—what’s novel is the on-treatment immune readout and the numerically higher ypN0 in the 9Gy arm.