RPS6KA1 and cancer: However, to date, drugs targeted to block p90RSK are not yet used in cancer clinics, despite the great variety of functions regulated by the different p90RSK isoforms and the fact that the chemical inhibition of this group of kinases has been shown to be effective in blocking the invasion and metastasis of several solid tumors in preclinical models [20], and even though there are many more recent examples of p90RSK involvement in tumor pathogenesis and resistance to conventional therapies.