CD4 and cancer: Despite increasing evidence supports that CD4+ T cells involved in MHC-II-mediated tumor killing potentially play a key role in anti-tumor immunity (Nagasaki et al., 2020; Oh et al., 2020; Sacher et al., 2020), studies focusing on the association between MHC-II signature and immune response or the prognosis of malignant tumors has not been thoroughly researched and reported.