PIK3CA and cancer: Upon further evaluation with orthogonal ultra-deep next-generation sequencing, no mutations in PIK3CA were found in any of multiple regions of the initial PTC sample, while the ATC metastases contained the mutation at high cancer cell fractions (>0.90), suggesting that tumor cells harboring the PIK3CA mutation may have been present in the initial disease but only in regionally subclonal populations that later seeded the ATC metastases.