PIK3CA and neoplasm: Accounting for the impact of trisomy 8 or loss of heterozygosity involving chromosome 8p, the relative mutant allele frequencies of FGFR1 versus PIK3CA or PIK3R1 were approximately equivalent in 7 of the 9 tumors, indicating that these two events were both likely to have occurred early during tumor evolution and were present clonally throughout all tumor cells.