PIK3CD and cancer: Our previous finding of mutations in several components of the PI3K pathway in UC, and the finding of PIK3R1 mutations in other cancer types, prompted us to search for mutations in PIK3R1. As evidence has emerged that that N-terminal domains of p85α have oncogenic functions, we chose to screen the entire coding sequence of PIK3R1, rather than focus on exons 12, 14 and 15.