Cytopathology of myxofibrosarcoma: a study of 66 cases and literature review.

Introduction: Myxofibrosarcoma is one of the more common sarcomas encountered in adults.
Materials and Methods: A search was made of our cytopathology and surgical pathology databases for cases diagnosed as myxofibrosarcoma (MyxoFS). FNA biopsy smears and cell block were performed and examined using standard techniques.
Results: Sixty-six cases were retrieved from patients aged 40 to 94 years (mean: 67 years), with a male:female ratio of 1.4:1. Forty-seven (71%) were primary neoplasms, 13 (20%) locally recurrent, and 6 (9%) metastasis. Lower extremity was the most common site 38 (58%) cases, followed by upper extremity and trunk (each 13 [20%] cases), 1 head/neck, and 1 pleural-based mass. Forty-two (64%) cases were specifically/correctly diagnosed as MyxoFS. Thirteen (20%) were diagnosed as undifferentiated pleomorphic sarcoma (UPS), 3 (4.5%) as myxoid neoplasm, 2 (3%) as myxoid sarcoma, and 1 (1.5%) sarcoma, not otherwise specified. As most were examples of high-grade (HG) MyxoFS, cytomorphology contained pleomorphic and spindled cells set in a variable amount of myxoid stroma. Arborizing capillaries were common, and pseudolipoblasts were uncommon. All cases interpreted as UPS were HG MyxoFS histologically. Five (7.5%) cases-pleomorphic liposarcoma (3), solitary fibrous tumor (1), and atypical lipoma (1)-were mistakenly diagnosed. Ancillary immunohistochemistry played a minor role in diagnostic assessment.
Conclusion: MyxoFS was accurately interpreted using FNA biopsy in about two thirds of cases. One fifth were misinterpreted as UPS due to the absence/near absence of myxoid stroma, which varies considerably in the definition of this neoplasm.
(Copyright © 2021 American Society of Cytopathology. Published by Elsevier Inc. All rights reserved.)