Naomi Frederick¹, M. Facey¹ 

¹Dorevitch Pathology, Ballarat, Australia.  

Introduction: Hepatic epithelioid haemangioendothelioma (HEH) is an extraordinarily rare vascular tumour of intermediate malignant potential, with a prevalence of <1 / 1,000,000. (1) It has slight predominance in middle aged females, however occurs over a wide age range. (2) Multifocal liver involvement is present in 75% of patients with HEH. (2) 

Case summary: Our case involves a 48 year old female, who presented with 3 incidentally identified liver lesions. The histology showed a tumour composed of epithelioid cells within a variably fibromyxoid stroma, with round to ovoid nuclei and intra-cytoplasmic vacuoles containing erythrocytes. Immunohistochemistry (IHC) showed diffuse strong ERG staining and CD31 positivity. The tumour demonstrated strong diffuse CAMTA1 staining on subsequent testing, consistent with HEH. 

Discussion: CAMTA1 is a highly specific and sensitive marker for HEH which reflects the driving WWTR1::CAMTA1 gene fusion present in up to 90% of cases. (WHO, 2024) A small subset of HEH demonstrates a YAP::TFE3 fusion resulting in positive TFE3 IHC. FISH may be performed for either fusion product in select cases. 

Conclusion: HEH is a rare tumour of unknown aetiology, arising in patients without known liver disease and with no identifiable risk factors. (2) 

 References: 

1. DePinieux et al. (2021, 2 25). Nationwide incidence of sarcomas and connective tissue tumors of intermediate malignancy over four years using an expert pathology review network. PLoS One, 16(2). doi:10.1371/journal.pone.0246958

2. WHO. (2024). Epithelioid Haemangioendothelioma. (J. Hornick) Retrieved 25/9/2024, from WHO Classification of Tumours: https://tumourclassification.iarc.who.int/chaptercontent/31/93