CD4 and breast carcinoma: Cancer-associated fibroblasts (CAFs) are the predominant cell type present; however, the breast cancer microenvironment is also populated by lymphocytes, macrophages, myeloid lineage cells, etc., which predominantly play roles in immune reactions.116,117 In the early stages of tumor development, the immune microenvironment mainly suppresses tumor proliferation through the cytokine environment produced by activated CD8+ and CD4+ T cells.