Table 1 summaries known mutant genes in both adenocarcinoma and squamous-cell carcinoma. The most commonly mutated gene is p53, seen in 45%–70% of adenocarcinomas and 60%–80% of squamous-cell carcinoma. Other aberrant genes, such as EGFR, KRAS, LKB1 and PTEN, are closely associated with the mTOR regulation network. Hence, we will discuss p53 in this section and mTOR pathway in Section 5. Here, KRAS is linked to adenocarcinoma.