In serum analysis, serum-napsin A in patients with primary lung adenocarcinoma was 16.1 (2.0–366.1) ng∙mL−1, and that in the control group was 23.3 (3.1–219.5) ng∙mL−1, indicating no significant difference (P = 0.251). Here, NAPSA is linked to lung adenocarcinoma.