IL-17B is widely produced in many cell types, including chondrocytes, neurons, intestinal epithelial cells, and breast cancer cells, whilst IL-17D is detected in various tissues, including brain, heart, lung, pancreas, skeletal muscle, and adipose tissue, but, in the immune system, IL-17D is restricted to naïve CD4+ T and B cells [5]. This evidence concerns the gene IL17D and breast cancer.