CPA4 and esophageal squamous cell carcinoma: Moreover, several studies have shown that CPA4 expression is increased in multiple cancer tissues, including tissues from patients with pancreatic cancer, gastric cancer, esophageal squamous cell carcinoma, and lung cancer, and may serve as a potential diagnostic and prognostic marker.11, 12, 13, 14 These findings suggest that CPA4 may play a crucial role in cancers; however, the role of CPA4 in lung tumorigenesis remains poorly understood.