PLK1 and squamous cell carcinoma: They later reported that bromelain treatment of human epidermoid carcinoma and melanoma cells, in vitro, resulted in cell cycle arrest at G(2)/M phase (by modulation of cyclin B1, phospho-cdc25C, Plk1, phospho-cdc2 and myt1) and subsequent induction of apoptosis through modulation of Bax-Bcl-2 ratio, apoptotic protease activating factor 1 (Apaf-1), caspase-9, and caspase-3 [33].