**Lyudmila V. Bel'skaya 1,\*, Elena A. Sarf 1, Denis V. Solomatin <sup>2</sup> and Victor K. Kosenok <sup>3</sup>**


Received: 14 November 2020; Accepted: 14 December 2020; Published: 15 December 2020

**Abstract:** The aim of the work was to study the features of the salivary biochemical composition in the combined pathology of lung cancer and chronic obstructive pulmonary disease (COPD) of varying severity (COPD I, COPD II). The study group included patients with lung cancer (*n* = 392), non-malignant lung pathologies (*n* = 168) and healthy volunteers (*n* = 500). Before treatment, the salivary biochemical composition was determined according to 34 indicators. Survival analysis performed by the Kaplan-Meier method. Biochemical parameters (catalase, imidazole compounds ICs, sialic acids, lactate dehydrogenase (LDH)) that can be used to monitor patients at risk (COPD I) for timely diagnosis of lung cancer are determined. A complex of salivary biochemical indicators with prognostic value in lung cancer was revealed. For patients with lung cancer without COPD, a group of patients with a favorable prognosis can be distinguished with a combination of ICs < 0.478 mmol/L and LDH > 1248 U/L (HR = 1.56, 95% CI 0.40–6.07, *p* = 0.03891). For COPD I, a level of ICs < 0.182 mmol/L are prognostically favorable (HR = 1.74, 95% CI 0.71–4.21, *p* = 0.07270). For COPD II, combinations of pH < 6.74 and LDH > 1006 U/L are prognostically favorable. In general, for patients with lung cancer in combination with COPD I, the prognosis is more favorable than without COPD.

**Keywords:**lung cancer; chronic obstructive pulmonary disease; saliva; biochemistry; diagnostics; prognosis
