Napsin A (aspartic protease A) belongs to the class of endopeptidases, which is mainly expressed in adult lungs (type II lung cells), kidneys and fetal lungs, and is low in adult spleen and peripheral blood leukocytes. Napsin A may be involved in the processing of lung cell surfactant precursors. Napsin A is expressed in more than 90% of primary lung adenocarcinoma, but not in other malignant tumors, so it can be used as a potential marker for primary lung adenocarcinoma.
