KRT19 and lung cancer: The most commonly used STM testing for lung cancer includes neuron‐specific enolase (NSE), carcinoembryonic antigen (CEA), cancer antigen 125(CA125), carbohydrate antigen 153(CA153), the soluble fragment of cytokeratin 19 (CYFRA21‐1), and squamous cell carcinoma antigen (SCC).7, 8, 14, 17