Metastatic perirectal PEComa treated by checkpoint inhibitor immunotherapy and multimodal treatment: case report and review of the literature.

Malignant PEComas are an extremely rare subtype of soft tissue sarcomas. Here, we report the case of a man presenting with a perirectal PEComa and liver metastasis. Since the tumor harbored a tumor mutational burden of 23/Mb and a programmed death-ligand 1 tumor positivity score of 50%, the patient was treated with pembrolizumab as a second line of systemic therapy, in combination with everolimus. This combined therapy led to a near-complete response of the primary tumor and a partial response of the metastasis. Radioembolization of the liver metastasis was performed due to isolated liver progression, and the pelvic tumor was treated by radiotherapy because of pelvic symptoms. The disease is still stable after 13 months of pembrolizumab plus everolimus and multimodal treatment. This case shows that malignant PEComas can display molecular features associated with sensitivity to checkpoint inhibitors. The use of checkpoint inhibitors may be a relevant therapeutic strategy in these patients. It is also the first report on selective internal radiation therapy in PEComas.