PTEN and chronic obstructive pulmonary disease: In addition, there was a significant positive correlation between the PTEN protein levels and airway obstruction measured by FEV1/FVC ratio (r = 0.65, P < 0.001) or the severity of air flow limitation by %FEV1 (r = 0.50; P < 0.01; Fig. 1C), indicating that the PTEN levels were decreased significantly as COPD progresses (Fig. 1D).