PIK3R1 and digestive system cancer: These, included PTEN, SPZ1, FBXW7 (with two mutation clusters each) and ADCY10, PIK3R1 and ARIDA (with one cluster each) in CYT-high rectum tumors; whereas in the CYT-low subgroup, TP53 was the only cancer driver with one mutation cluster (Fig. 3h).