Idiopathic pulmonary fibrosis, pulmonary silicosis and lung cancer

The presence of idiopathic pulmonary fibrosis (IPF) and pulmonary silicosis (PS) has been reported to increase lung cancer risk. The incidence of lung cancer is increased 7- to 10-fold in patients with IPF and 2- to 3-fold in patients with PS. Most tumors including squamous cell carcinoma are located in the peripheral regions of the lung in both groups, indicating fibrosis-related origin. Why is the incidence of lung cancer higher when fibrotic disorders are present? In this paper, we discuss the mechanism by which IPF might contribute to an increased risk of lung cancer. Although the underlying mechanism is complicated, we consider the following possibilities: 1) occupational and environmental exposures might increase risk for both apparent IPF and lung cancer, 2) cell death in bronchial and alveolar epithelium and cell proliferation occur continuously in IPF, thereby playing a role in fibrosis associated with the increased incidence of lung cancer, and 3) 3p and 9p LOH is frequently identified in atypical epithelia from IPF, suggesting premalignant lesions. Further mechanism-oriented research on the association of lung cancer and fibrotic disorders is needed.