PIK3CA and cancer: Multiple mechanisms may be involved in PI3K mutation and aberrant activation in human cancers (Samuels and Ericson, 2006; Engelman, 2009; Jaiswal et al., 2009; Vanhaesebroeck et al., 2010; Cheung et al., 2011; Cancer Genome Atlas Research Network, 2012; Walter et al., 2018).