Several evidences allow to hypothesize that ROS could play a primary role in anticancer activity of nelfinavir: a) the presence of high necrotic cell percentage following nelfinavir short-term treatment in breast cancer cells; b) the observation that HSP90 is sensitive to oxidation [66, 67]; c) clinical studies on nelfinavir as anti-viral drug that revealed an involvement of ROS in side effects onset [74–78]. This evidence concerns the gene HSP90AA1 and breast carcinoma.