TTF1 and adenocarcinoma: Given the high frequency of EGFR mutations in these double-positive cases (3/7, 43%), we speculated that the double-positive adenocarcinomas were of the TRU-type and that TTF-1-positive TRU-type adenocarcinomas were induced to express HNF4α through the local loss of TTF-1 (e.g., by epigenetic silencing).