The most frequently altered genes were KRAS (mutated in 29% of adenocarcinoma and 1.9% of squamous cell carcinoma patients), EGFR (mutation in 6.7% of adenocarcinoma and 1.9% of squamous cell carcinoma but amplification in 2.3% of adenocarcinoma and 8.6% of squamous cell carcinoma patients) and TP53 (9.3% of adenocarcinoma and 21.1% of squamous cell carcinoma). Here, KRAS is linked to squamous cell carcinoma.