CD8A and melanoma: A previous investigation, employing flow cytometry to analyze TIL extracted from biopsy specimens of malignant melanoma (n = 12), non-small cell lung cancer (n = 27), and gastric cancer (n = 48) before anti-PD-1 monotherapy, demonstrated that the ratio of PD-1+CD8+ T cells to PD-1+ Treg cells in the tumor microenvironment could predict the clinical efficacy of anti-PD-1 monotherapy [17].