A, Nο correlation was found between pathologic response in primary tumor and visualization of radiologic immune-related adverse effects (irAEs) on the T1 fluoro-[18F]-deoxy-2-D-glucose positron emission tomography/computed tomography (FDG-PET/CT). B, Change in maximum standardized uptake value (SUVmax) of the most FDG-avid metastatic cervical lymph nodes between T0 and T1 was not different between participants with (median 14%, range −11% to 75%) and without radiologic irAEs (median 20%, range −48% to 35%, ESwrs = −5% [90% CI, –20% to 45%] for with or without) after preoperative immunotherapy. C, Primary oral cavity squamous cell cancer (OCSCC) SUVmax increased more in participants with (median 34%, range −5 to 47%) vs without (median −1%, range −29 to 25%, ESwrs = 30% [90% CI, 6% to 67%] for with or without) radiologic irAEs on T1 FDG-PET/CTs.