CD4 and breast cancer: In HER2 + breast cancer, the peripheral blood immune phenotype did not differ according to NAC response.<h4>Conclusions</h4>Pre-treatment peripheral blood immune cell populations (myeloid in TNBC; CD8 + naïve T cells and CD4 + T<sub>EMRA</sub> cells in luminal breast cancer) were associated with response to NAC in early-stage TNBC and hormone receptor-positive breast cancers, but not in HER2 + breast cancer.<h4>Trial registration</h4>NCT02022202 .