SELL and neoplasm: Our comprehensive analysis of lymphocyte composition in the gastric mucosa revealed that: i) the proportion of CD8+/CD3+ cells was relatively higher in the peri-tumor mucosa than in the background mucosa; ii) the proportion of CCR4+/CD3+ cells was higher, and the ratio of CD62L+/CD3+CD4+ cells was relatively lower in the gastric mucosa of cancer patients than in non-cancer patients; and iii) the proportion of CD45RA−CD62L+/CD3+CD4+ cells, namely, the central memory CD4+ T-cell fraction, was lower in the gastric mucosa of cancer patients than in non-cancer patients.