Because multiple genes that encode proteins in the EGFR signaling pathway have been found to be mutated in lung adenocarcinomas, we specifically sought to identify potential gain-of-function mutations in gene families in this pathway, i.e. in ERBB1-4, PIK3CA, AKT1-3, FRAP1, RPS6K1-2, RAS (K-, N-, and H-), RAF (A-, B-, C-), MAP2K1-2, and MAPK-1-3. The gene discussed is PIK3CA; the disease is lung adenocarcinoma.