CD4 and breast carcinoma: First, mRNA levels of three cytokines were measured in the mammary tumors: (i) IL-6 that induces differentiation of activated CD4+ T helper cells toward inflammatory Th17 cells, (ii) IL-17c that is secreted from Th17 cells and is expressed only in activated T cells where it promotes inflammation in the tumor microenvironment and enhances tumor growth, and (iii) IL-17f that induces inflammation and is associated with breast cancer progression, metastasis, and poor overall survival (Coffelt et al. 2015).