[Clinicopathological features of primary pulmonary epithelioid hemangioendothelioma: a study of 7 cases].

<b>Objective:</b> The clinicopathological features of pulmonary epithelioid hemangioendothelioma (PEHE) were analyzed to provide guidance for clinical practice. <b>Methods:</b> The clinical manifestations, imaging examination, pathological morphology and molecular characteristics, treatment and prognosis of patients with pulmonary epithelioid hemangioendothelioma were retrospectively collected. All cases were admitted to Fujian Medical University Union Hospital from January 2012 to May 2023. <b>Results:</b> Of 7 PEHE cases, 2 underwent tumor biopsy and 5 underwent tumor resection. There were 4 males and 3 females, with a median age of 58 years old. Six cases showed multiple bilateral nodules, and only one case showed a single lesion in the lower left lung lobe. Five patients presented with respiratory symptoms, like cough, sputum, hemoptysis, shortness of breath. There were round-like solid lesions with clear border and homogeneous density on lung CT. Histologically, it showed nodular growth with a distinctive myxohyaline stroma. Necrosis was seen in the center of some cases. Epithelioid tumor cells were arranged in cords, solid pattern or single cells, with abundant eosinophilic cytoplasm and occasional intracytoplasmic vacuoles. The plasmacytoid nucleus were round to oval in shape with obvious nucleoli, minimal pleomorphism and few mitoses. The tumor cells were positive for vascular endothelial markers: CD31 (7/7), CD34 (5/7), ERG (6/6), and Fli-1 (5/6); CKpan was focally positive in 3 cases (3/7), and TFE3 in 2 cases. Ki-67 index ranged from 5% to 10%. Additionally, the tumor cells partially express PD-L1 in two cases. Moreover, lung carcinoma-related gene detection was negative in one case. The TFE3 break-apart probe in two cases did not display a split signal. In terms of treatment, 4 cases were treated with surgery, 1 case was treated with chemotherapy and surgery, and 2 cases were follow-up observation. After the median 34.4 months follow-up time, one was lost to follow-up, six were survived. Their CT scans showed slight enlargement of pulmonary nodules without other organ metastases. <b>Conclusions:</b> PEHE is a rare vascular-derived tumor, which is usually characterized by multiple solid bilateral nodules with slow growth. It tends to lack specific clinical symptoms, and is prone to be misdiagnosed as a metastatic carcinoma. Diagnosis primarily rely on pathology, with the use of an immunohistochemical package being crucial for definitive and differential diagnosis.