# A Case Report of Metastatic Retroperitoneal Angiosarcoma Mimicking Reactive Angioendotheliomatosis

## TL;DR

A case of metastatic retroperitoneal angiosarcoma was initially mistaken for reactive angioendotheliomatosis but was correctly diagnosed after further investigation.

## Contribution

The paper presents a novel case highlighting diagnostic challenges between angiosarcoma and reactive angioendotheliomatosis.

## Key findings

- Initial histopathology suggested reactive angioendotheliomatosis but was inconclusive.
- Further imaging and immunohistostaining confirmed metastatic retroperitoneal angiosarcoma.
- The case underscores the importance of thorough diagnostic evaluation for accurate cancer classification.

## Abstract

Angiosarcoma is a malignant proliferation of vascular and lymphoendothelial origin. In terms of pathology outlines, this entity may resemble other growths derived from blood vessels. Reactive angioendotheliomatosis, an intravascular proliferation, is frequently hard to discern histologically from angiosarcoma. In this study, we outline a case initially presenting with features supporting reactive angioendotheliomatosis. Clinical progression and inconclusive histopathology raised suspicion, and further investigation was decided. Computed tomography imaging revealed a large retroperitoneal tumor, and subsequent surgery with additional histological examinations of the excised mass and cutaneous samples was performed, along with immunohistostaining. As a result, diagnosis and prognosis pointed to an entirely different direction.