An approach to pleomorphic sarcomas: can we subclassify, and does it matter?

Area of Science:

• Oncology
• Pathology
• Surgical Pathology

Background:

• The term malignant fibrous histiocytoma (MFH) has been largely replaced by undifferentiated pleomorphic sarcoma (UPS) in current classifications.
• However, a significant number of pleomorphic neoplasms are still diagnosed as UPS, potentially masking specific lines of differentiation or other tumor types.
• Some cases diagnosed as UPS may represent pseudosarcomas, such as sarcomatoid carcinomas, highlighting diagnostic challenges.

Purpose of the Study:

• To provide a historical overview of malignant fibrous histiocytoma (MFH) and undifferentiated pleomorphic sarcoma (UPS).
• To offer a systematic approach for evaluating pleomorphic malignant neoplasms.
• To discuss the utility of ancillary diagnostic techniques in accurately classifying these challenging tumors.

Main Methods:

• Review of historical literature and current classification systems for soft tissue sarcomas.
• Discussion of histopathological features distinguishing true pleomorphic sarcomas from other entities.
• Emphasis on the role of immunohistochemistry and other ancillary studies in differential diagnosis.

Main Results:

• MFH is an outdated term; UPS is the current designation for pleomorphic sarcomas lacking clear differentiation.
• A subset of tumors classified as UPS may possess specific differentiation, requiring precise subclassification.
• Sarcomatoid carcinomas are a common mimic of UPS and must be differentiated using appropriate diagnostic tools.

Conclusions:

• Accurate classification of pleomorphic malignant neoplasms is crucial for appropriate patient management and treatment.
• Distinguishing true UPS from sarcomatoid carcinomas and other entities relies on a combination of morphology and ancillary studies.
• This review provides a framework for pathologists to navigate the complexities of diagnosing and classifying UPS and related tumors.