The application of PCR in diagnostic gene mutation analysis, such as the B-raf proto-oncogene (BRAF), EGFR, Kirsten rat sarcoma viral oncogene homolog (KRAS), neuroblastoma RAS viral oncogene homolog (NRAS), and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) genes from the blood, is meaningful in initial cancer stratification and the monitoring of cancer progression. This evidence concerns the gene PIK3CA and cancer.