Tumor-infiltrating lymphocytes, in particular CD8+ cells and CD20+ cells, were strongly associated with survival in different carcinomas (Nielsen et al., 2012; Edin et al., 2019; Hee Yeon et al., 2019; Kuroda et al., 2021) and canine glioma (Krane et al., 2021), but the role of CD20+ B cells was not reported in canine breast cancer. Here, CD8A is linked to breast cancer.