(Intravascular) papillary endothelial hyperplasia or Masson's tumour of the axilla in a patient with a history of breast cancer.

Intravascular papillary endothelial hyperplasia, or Masson's tumour, is a benign lesion of the subcutaneous tissue and skin, characterised by a reactive proliferation of endothelial cells within a vessel. Although this pathology can occur at various sites, it is generally rare. Differential diagnosis with other benign lesions or malignancies can be challenging, and since its circumscribed nature is impossible to recognise with a biopsy, excision is frequently required.We present the case of a female patient with a history of bilateral breast cancer, treated with surgery, chemotherapy and radiotherapy, who developed a slowly growing, large bulging mass in the right axilla. Biopsies were benign, and the positron emission tomography-CT showed no hypermetabolism of the mass. However, due to the debilitating bleeding from the fragile mass and uncertainty about its biological behaviour, excision was performed. Pathological examination revealed an intravascular lesion with a central thrombus, characteristic of intravascular papillary endothelial hyperplasia.