MTOR and melanoma: The promising results of our previous research (Ciołczyk-Wierzbicka and Laidler 2018; Ciołczyk-Wierzbicka et al. 2018, 2019, 2020) on inhibition of invasion and activation of the apoptosis process with the use of nanomolar concentrations of everolimus, the first-generation mTOR inhibitor, encouraged us to investigate the effect of three generations of mTOR kinase inhibitors on activation of caspase 3, the apoptosis process, and proliferation in melanoma cells.