Coal workers' pneumoconiosis (CWP), commonly known as black lung disease, is an occupational lung disease caused by prolonged inhalation of coal mine dust. Coal dust is a complex mixture of carbon particles, silica, kaolin, ite, and other minerals. When inhaled, particles smaller than 5 micrometers penetrate to the terminal bronchioles and alveoli, where they are phagocytosed by alveolar macrophages. The carbon-laden macrophages, called dust macrophages, accumulate around respiratory bronchioles and form coal macules -- small (1-5 mm) aggregates of dust-laden macrophages surrounded by a small amount of reticulin and collagen fibers. These coal macules are the fundamental pathological lesion of simple CWP. The associated dilatation of respiratory bronchioles surrounding coal macules is termed focal emphysema. Simple CWP is characterized by numerous small coal macules (less than 10 mm) distributed predominantly in the upper lobes of the lungs. Simple CWP typically causes minimal functional impairment and may be asymptomatic, detected only on routine screening chest X-rays. However, in approximately 1-5% of cases, simple CWP progresses to complicated CWP, also known as progressive massive fibrosis (PMF). PMF is defined by the development...