Serum surfactant protein D predicts the outcome of patients with idiopathic pulmonary fibrosis treated with pirfenidone

Background: Idiopathic pulmonary fibrosis (IPF) is a fatal pulmonary disease with poor prognosis. Pirfenidone, the first antifibrotic drug, suppresses the decline in forced vital capacity (FVC) and improves prognosis in some, but not all, patients with IPF; therefore, an indicator to predict the therapeutic effect of pirfenidone is desirable. Objectives: To clarify whether baseline parameters can be predictors of disease progression and long-term prognosis in patients with IPF treated with pirfenidone. Methods: We retrospectively investigated patients with IPF who started treatment with pirfenidone between December 2008 and November 2014 in our Hospital. Patients who were treated with pirfenidone for more than 6 months were enrolled in this study and were observed until November 2015. We investigated the relationship of clinical characteristics, pulmonary function test results, and blood examination results at the start of pirfenidone with the outcome of patients. Results: Sixty patients were included in this study. In multivariate logistic regression analysis, % predicted FVC and the serum surfactant protein (SP)-D level were predictors of a 10% or greater decline in FVC in the initial 12 months. In the Cox proportional hazards model, these two factors also predicted progression-free survival. Smoking status, % predicted diffusing capacity for carbon monoxide, and the SP-D level predicted overall survival. Conclusions: The serum SP-D level was an independent predictor of disease progression and prognosis in patients with IPF treated with pirfenidone. Thus, responders to pirfenidone can be defined more precisely by measuring the SP-D level.