PIK3CA and head and neck squamous cell carcinoma: Investigation of selected cancer-related pathways (40) showed medium correlations of 0.4 to 0.5 for most pathways, including the PI3K pathway, DNA damage repair (HR and NER, NHEJ), Notch pathway, Wnt pathway, etc. In agreement with the global protein-RNA analysis, lung cancers (squamous cell carcinoma, LUSC and adenocarcinoma, LUAD) and head and neck cancer (HNSCC) presented the highest protein–RNA correlations for most individual pathways, while ovarian cancer and renal cancer (CCRCC) showed the lowest ones.