In 1 patient with regionally advanced melanoma, a CD8 PET/CT scan acquired 28 d after initiating immunotherapy (pembrolizumab) demonstrated marked 89Zr-Df-IAB22M2C uptake in 2 nodal metastases in the left axilla (SUVMAX of 9.5 and 10.0) (Fig. 4), suggesting that the patient had a high degree of CD8+ leukocyte infiltration in the tumor; follow-up CT imaging in this patient demonstrated a complete response to therapy, which has lasted 2.3+ years. This evidence concerns the gene CD8A and melanoma.