In multidrug-resistant CRC, PI3K signalling is prolonged by PIK3CA mutations, null mutation of PTEN, and RAS mutations upon treatment with standard chemotherapeutic drugs and targeted therapeutic agents (Laurent-Puig et al., 2009; De Roock et al., 2010; Kim et al., 2013; Hamada, Nowak & Ogino, 2017). The gene discussed is PIK3CD; the disease is colorectal carcinoma.