MUC1 and neoplasm: Key markers for alveolar dysfunction include Krebs von den Lungen-6 (KL-6), mucins (MUC-1, MUC-4, MUC-5, MUC-16), tumor markers (CA 15-3, CA 125, CA 19-9), surfactant proteins (Sp-A, Sp-D), and club cell secretory protein (CC16).