The immunohistochemical results were as follows: CK (weak+), CK7 (−), Napsin A (−), TTF−1 (−), Vimentin (+), P40 (−), Ki-67 (accounting for approximately 70%), Factor VIII (+), CD31 (+), and HMB-45 (−) (Figure 2) According to the diagnostic criteria in literature, the positive expression of vascular endothelial markers like CD31 and Factor VIII and the specific morphological features of tumor cells under the microscope are crucial for the diagnosis of pulmonary epithelioid hemangioendothelioma (PEH) (2). This evidence concerns the gene PECAM1 and neoplasm.