All clinical and pathological parameters were collected by chart review. The criteria for inclusion in the LC group were as follows: 1. histopathological diagnosis of laryngeal squamous cell carcinoma; 2. regular smoker; and 3. data on clinical parameters [e.g. tumour (T), node (N), metastasis (M) classification, and location of tumour, according to the AJCC Cancer Staging Manual, 8th Edition] 10 . The criteria for inclusion in the control group were as follows: 1) no history of malignancy; 2) regular smoker; 3) undergoing septoplasty surgery at the otolaryngology clinic; 4) a normal laryngeal examination prior to surgery. In both groups, patients with a history of use of ACE inhibitors and/or AT receptor blockers and patients with genetic diseases involving predisposition to malignancy were excluded. Descriptive information was collected on the age, gender, tumour localisation, TNM classification and stage. The frequency of II, ID and DD genotypes and I/D alleles of the ACE gene in patients diagnosed with LC were compared with the control group. In addition, the clinical findings of patients diagnosed with LC were analysed in terms of genotype and allele frequency. For genetic analysis, 4 cc venous blood was taken from all patients in the study group into tubes containing EDTA during routine preoperative examinations. Samples were stored at -20°C in the medical genetics laboratory until DNA isolation.