PDCD1 and neoplasm: Researchers determined a ratio (Ki67 + PD-1 + CD8 + T cell to tumor burden) of 1.94 by classification and regression tree analysis [33], which turned out to strongly differentiate patients with different clinical outcomes as early as week 6 post-treatment; the ratio > 1.94 was correlated with better outcomes in overall response rate, PFS, and OS (P < 0.05).