Immunohistochemical analysis of a merkeloma observed in a patient affected byhereditary haemorrhagic telangiectasia.

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterised by
epistaxis, telangiectases, and multiorgan vascular dysplasia. Mutations of the ENG and ACVRL1 genes
cause at least 80% of cases. We report the first case of merkeloma found in a patient with HHT carrying
an ENG mutation. We analysed the tumour with immunohistochemical methods using primary
antibodies against CD105 (endoglin), TGF-β, Smad4, CD31 and CD34. Tumour cells were positive for
Smad4, weakly positive for TGF-β, and negative for CD105. Vasal endothelial cells were highly positive
for CD105, CD31 and CD34. No remarkable differences between cancer and normal cells in our patient
or between the patient’s merkeloma and two control merkelomas were observed. The presence of a
merkeloma in an HHT patient could be an occasional association, but to certainly assume it further
investigations are needed.