Classification and a practical pattern-based approach to the diagnosis of adipocytic tumors

Abstract

Adipocytic tumors are among the most common mesenchymal neoplasms in general surgical pathology. These tumors encompass a broad histological spectrum with variable degrees of adipocytic differentiation and a wide range of clinical behaviour, varying from entirely benign lipomas to aggressive pleomorphic liposarcomas. The World Health Organization (WHO) classification of adipocytic tumors has evolved considerably in the last decades, largely due to important advances in understanding their pathogenetic basis. Although classic examples of lipomas and liposarcomas are straightforward diagnoses, primarily distinguished by their morphological characteristics, several lipomatous tumors are now known to show unique, recurrent molecular genetic aberrations, identification of which can be used in the diagnostic work-up of distinct (uncommon) lipomatous tumor variants and histologically ambiguous adipocytic tumors. This article will provide a practical pattern-based approach to the histological diagnosis of benign, intermediate and malignant adipocytic neoplasms. We will focus on the currently known morphological, immunohistochemical and molecular features of the different adipocytic tumor entities, discuss their differential diagnoses and update on recently described adipocytic tumor entities (lipoblastoma-like tumor, atypical spindle cell/pleomorphic lipomatous tumor, and myxoid pleomorphic liposarcoma).