INTRODUCTION

Cells and tissue sampled from this group of neoplasms is easily recognized as malignant but definitive subtyping is often difficult or impossible. The majority of sarcomas falling within this group are pleomorphic liposarcomas and neoplasms originally designated as pleomorphic malignant fibrous histiocytomas. The latter group is now more commonly designated as pleomorphic undifferentiated sarcoma (PLUS). This designation is given after extensive immunohistochemical and even molecular diagnostic studies have failed to determine a precise histologic type.

Sarcomas within this category can be confused with melanoma and anaplastic carcinoma. Lymphomas rarely enter the differential diagnosis of pleomorphic sarcoma but pleomorphic carcinomas from a variety of sites may enter the differential diagnosis for material aspirated from these neoplasms. Pleomorphic, giant cell, and sarcomatoid carcinomas occur in the lung, kidney, thyroid, and pancreas. Clinical history, immunohistochemistry, and molecular diagnostics are often of help in recognizing carcinomas within the differential diagnosis of pleomorphic sarcoma.

In addition to pleomorphic liposarcomas and pleomorphic high grade sarcoma (malignant fibrous histiocytoma), pleomorphic rhabdomyosarcoma, dedifferentiated liposarcoma, dedifferentiated chondrosarcoma, pleomorphic leiomyosarcoma, and some cases of malignant mesenchymoma fall within this category. The majority of these sarcomas occur in adults, often in late adult life.