HTR4 and chronic obstructive pulmonary disease: Several lines of evidence suggest that biological processes resulting in pulmonary impairment warrant consideration as independent lung cancer risk factors, including observations that previous lung diseases influence lung cancer risk independently of tobacco use6,8–10, and overlap in genetic susceptibility loci for lung cancer and chronic obstructive pulmonary disease (COPD) on 4q24 (FAM13A), 4q31 (HHIP), 5q.32 (HTR4), the 6p21 region, and 15q25 (CHRNA3/CHRNA5)11–14.