Panitumumab (EGFR) Maintenance: Spatial Immune Markers Predict Benefit in RAS-WT mCRC

Panitumumab, an anti-EGFR IgG2, was tested as FU/FA maintenance (±Pmab) after Pmab+FOLFOX induction in PanaMa; this translational analysis profiled 12 immune markers in tumor/stroma compartments from resections (n=194; NCT01991873). Low CD163 and high PD-1 in the tumor center independently associated with longer PFS; high central LAG3 tracked with better OS. Patients with low invasive-margin CD3/CD8 and central LAG3/CD163 (and low Immunoscore) but high central CD45RO derived more PFS benefit from Pmab, and an Immunoactivation Score ≥ 2 predicted both PFS (HR 0.50, 95% CI 0.32–0.76) and OS (HR 0.54, 0.33–0.86) gains—consistent with the parent trial’s FU/FA+Pmab advantage (mPFS 8.8 vs 5.7 mo; HR 0.72) and VALENTINO’s finding that panitumumab alone is inferior to FU/FA+Pmab for maintenance.