Carcinoma of the lung and cigarette smoking. Effect on serum ribonuclease activity

Serum ribonuclease levels were determined in 54 patients with lung carcinoma, 74 long-term cigarette smokers, and 172 nonsmokers. The mean serum ribonuclease level was significantly higher in patients with lung carcinoma and long-term smokers compared with healthy nonsmokers (P less than .001). The serum ribonuclease activity level was not related to chronological age, sex, or race of the smoker or nonsmoker population. Forty (75%) of 53 patients with lung cancer and 49 (66%) of 74 smokers had elevated serum ribonuclease levels compared with 13 (7%) of 179 nonsmoker healthy controls (P less than .001). The highest incidence of elevation was noted in patients with epidermoid carcinoma (95%).