CDKN2A and cancer: In both CHRNB4-high and -low subgroups, we observed deep copy number deletion of the tumour-suppressor genes CDKN2A and CDKN2B in ≈40% of smoking patients [49] and high-level copy number amplification of the oncogenes FADD and CCND1 in ≈35% of smoking patients [49], which contributed to cancer cell survival and proliferation in smoking patients.