PIK3R1 and neoplasm: Comparing the relative FGFR1 and PIK3CA/PIK3R1 mutant allele frequencies in RGNT when accounting for the impact caused by trisomy 8 or loss of heterozygosity involving chromosome 8p, we find that the FGFR1 mutation is uniformly clonal and present in all tumor cells as an early or initiating event, whereas the PIK3CA or PIK3R1 mutations either arise at a similar timepoint or occasionally as a later event during tumor evolution after FGFR1 mutation.