Mass General Brigham May 14 2025 Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States, most often caused by cigarette smoking or long-term exposure to air pollutants. While there is no cure, progression can be slowed by reducing exposure to these factors.  A new study from Mass General Brigham researchers uncovered another factor linked to progression of the disease: the accumulation of mucus in the lungs. People with COPD who had persistent