In multivariable analysis, several patient-related variables (age, body mass index (BMI), cancer), treatment-related variables (maintenance azithromycin, theophylline), clinical variables (sputum volume and body temperature) and laboratory results (C-reactive protein (CRP) levels) were associated with in-hospital antibiotic use independent of sputum purulence, neutrophil counts, inhaled corticosteroids and intensive care unit of which CRP level was the strongest determinant. The gene discussed is CRP; the disease is cancer.