Because previous studies have shown that increased cyclo-oxygenase-2 (COX-2) expression occurs preferentially in non-small cell lung cancers, and particularly, in adenocarcinomas and squamous cell carcinomas (Hida et al, 1998; Wolff et al, 1998; Ochiai et al, 1999), we analysed the association between aspirin use and lung cancer risk in a subset of 62 non-small cell lung cancer cases and 618 matching controls. Here, PTGS2 is linked to squamous cell carcinoma.