HSD17B1 and breast neoplasm: In addition, HSD17B1 has long been known to be under the positive stimulatory influence of growth factors like insulin-like growth factors Types I and II and retinoic acid and immunological factors like interleukin 1 (IL-1), IL-6 and tumor necrosis factor α (TNFα) and it is possible that the cells of the immune system are an important source of the factors that modulate the expression and activity of HSD17B1 is breast tumors [53].