Technicians tell lung adenocarcinoma from other cancers by looking at cells under a microscope. Lung adenocarcinoma starts in glandular cells, which make for example mucus. Lung adenocarcinoma usually grows in smaller airways, such as alveoli, the pockets at the ends of the lung. Lung adenocarcinoma is usually located more along the outer edges of the lungs. Lung adenocarcinoma tends to grow more slowly than other lung cancers.