The common downregulated genes in SCC and ADC included SFTPC, CLDN18, CHIAP2, SLC6A4, CD300LG, RS1, AGER, and MYOC. Majority of these genes are mainly involved in differentiation, cell death, cell cycle progression, regulation of immune response, migration, and lung adenocarcinoma formation [28,29,30]. Here, SLC6A4 is linked to AIDS dementia complex.