Agahozo MC, et al. - Ductal carcinoma in situ-associated tumor-infiltrating lymphocyte (TIL) density was assessed on the basis of the hematoxylin and eosin-stained sections from 473 individuals by the researchers in order to examine ductal carcinoma in the situ-associated immune response by identifying immune cell subsets according to ductal carcinoma in situ subtypes. A total of 131/473 individuals were viewed as TIL-high. In HER2+ and triple-negative ductal carcinoma in situ, the percentage of TIL-high cases was significantly greater. Overall, no statistical variation in immune cell composition according to subtypes was determined. Nevertheless, individual subtype comparison exhibited that ER+ HER2+ cases had a significantly greater proportion of CD8+ T cells as that of triple-negative cases. In TIL-high cases, PD-L1-SP142 expression on tumor cells was correlated with subtype and the least number of positive cases was noted in the HER2+ subtype (independent of ER). Although, PD-L1 expression by both clones was limited, in TIL-high ductal carcinoma in situ. Hence, in HER+ and triple-negative ductal carcinoma in situ, high numbers of TILs were predominantly noted. In comparison with the triple-negative subtype, the ER+ HER2+ subtype appeared to draw a greater proportion of CD8+ T cells. The HER2+ subgroup had the lowest PD-L1-SP142 expression on tumor cells among TIL-high cases. Moreover, this inferred a more obvious antitumor immunity in HER2+ ductal carcinoma in situ, which could play a part in its biological behavior.