In a prospective study of 77 patients with IPF, the correlation between baseline serum levels of KL-6 and the incidence of AE was evaluated; thirteen patients (17%) experienced AE during follow-up and baseline serum KL-6 levels were significantly higher in patients who developed AE than in patients with stable IPF. The gene discussed is MUC1; the disease is idiopathic pulmonary fibrosis.