Definitions of disease: Should possible and probable idiopathic pulmonary fibrosis be enrolled in treatment trials?

Idiopathic pulmonary fibrosis (IPF) is a chronic, fibrosing interstitial lung disease of unknown etiology characterized by progressive lung scarring and a median survival of 3–5 years from the time of diagnosis. The most recent consensus guidelines adopt a diagnostic process that characterizes patients as having a final diagnosis of IPF, probable IPF, or possible IPF determined from a combination of the clinical context and specific chest imaging and histologic disease patterns. Based on currently available data, the enrollment criteria for treatment trials could be expanded to include not only patients with IPF but also those with probable and possible IPF without adversely affecting trial design or outcomes.