INS and breast neoplasm: Several biological mechanisms by which physical activity is suggested to act on breast tumor development have been proposed [21,22], including lowering levels of endogenous sex hormones [23], modulating insulin and insulin-like growth factors, enhancing immunity, and reducing chronic inflammation [22], and it is possible that different intensities of physical activity during specific periods of life (eg: adolescence, premenopause, postmenopause) invoke distinct pathways to influence breast cancer risk.