KRT19 and squamous cell lung carcinoma: Cytokeratin 19 fragment detection has high diagnostic value in non–small cell lung cancer, especially in lung squamous cell carcinoma patients,[15] but its sensitivity is poor.[16] Therefore, this case warns us that when a patient’s chest image is lumpy with high-density shadows, accompanied by elevated serum tumor markers, we should not limit the diagnosis to lung cancer, but also consider the possibility of infectious disease.