PIK3CA and Merkel cell skin cancer: While 21/28 clinical trials and case reports identified here investigated the efficacy of TKIs and SSAs in reducing tumor volume for patients with MCC (Table S1), laboratory studies also revealed antiapoptotic inhibitors, epigenetic modifiers, p53 activators, PI3K inhibitors, and many other agents to be effective at promoting apoptosis in MCC cell lines as well.