PIK3CA and head and neck squamous cell carcinoma: They show that for HNSCC and breast cancer, the PIK3CA gene mutation detection tests were conducted in various biological materials (FFPE, serum, plasma, frozen tissue, cell lines) and with the use of various research techniques (RT-qPCR, Sanger sequencing, NGS, ddPCR) which affected the received sensitivity of detected changes [19,20,23,47,48,49,50,51,52,53,54,55,56].