A number of studies have shown a high incidence of lung cancer in patients with idiopathic pulmonary fibrosis (9.8 to 38%) compared to control subjects (2 to 6.4%). A similar trend occurs in other entities that affect the interstitial lung compartment, such as systemic sclerosis and sarcoidosis, as well as occupational diseases. The pathogenesis of lung cancer in patients with diffuse pulmonary fibrosis is still unclear. Recent progress in molecular and cellular biology has shed some light on the possible interactions of several types of inflammatory cells, following the deleterious effects of toxic factors leading to alveolitis, and destruction and disorganization of lung parenchyma, which results in fibrosis. Further research in the field would enhance our understanding of the pathogenic mechanisms of cancer development in these patients, and to explain the reason for the different incidence of lung cancer in patients with various interstitial lung diseases.