This transcript reviews the pathology of a Myxofibrosarcoma (MFS) presenting as a leg mass in a 60-year-old man. The discussion focuses on the diagnostic microscopic features, grading, and clinical implications of this relatively common soft tissue sarcoma. Key morphological findings include an extensive mixoid background with entrapped fat, scattered pleomorphic and atypical cells, and characteristic elongated, "curvilinear" vessels. The presence of pseudolipoblasts—tumor cells that have absorbed the surrounding hyaluronic acid—is also highlighted. Clinically, MFS is noted for its highly infiltrative growth pattern, which complicates surgical margin clearance and results in a high rate of local recurrence. Although low-grade MFS rarely metastasizes, recurrence may lead to dedifferentiation into higher grades, increasing the risk of metastasis.
Myxofibrosarcoma (MFS) Pathology Review
0:00 Case Introduction: The case involves a 60-year-old man presenting with a leg mass.
0:17 Mixoid and Infiltrative Growth: The tumor exhibits a significant mixoid background, entrapping background fat (adipocytes) rather than incorporating fat as a neoplastic element. This infiltration is characteristic of MFS.
0:50 Diagnostic Criteria: A diagnosis of Myxofibrosarcoma requires the presence of scattered atypical, hyperchromatic, or pleomorphic cells within the mixoid background.
1:27 Key Feature: Curvilinear Vessels: MFS often displays prominent, elongated, "curvilinear" or snake-like vessels running through the mixoid matrix.
1:40 Grading (Grade 1 MFS): Low cellularity and scattered pleomorphic cells indicate a Grade 1 MFS (sometimes referred to as low-grade).
1:52 Nomenclature Warning: The speaker advises against confusing Myxofibrosarcoma (MFS) with Low-Grade Fibromyxoid Sarcoma (LGFMS), noting their completely unrelated nature despite similar names.
2:27 Higher Grades: Grade 2 MFS involves cells clustering along vessels, while Grade 3 MFS features solid sheets of high-grade, undifferentiated pleomorphic sarcoma (UPS)-like morphology mixed with mixoid areas.
2:46 Clinical Context: MFS is relatively common among sarcomas, typically affecting the extremities of elderly patients. Approximately half of cases arise superficially (above the fascia, in the dermis or subcutis).
3:21 High Recurrence Rate: The tumor is highly infiltrative, "oozing" along subcutaneous septa and fascia, making complete surgical resection difficult and resulting in a high rate of local recurrence.
3:54 Prognosis and Progression: While Grade 1 tumors rarely metastasize, repeated local recurrence can lead to the tumor progressing to a higher, more aggressive grade, increasing the risk of distant metastasis.
4:09 Key Feature: Pseudolipoblasts: Characteristic "bubbly cells" (pseudolipoblasts) are present. Unlike true lipoblasts, the vacuoles in these cells contain hyaluronic acid (the blueish mixoid background substance) rather than clear fat.
5:15 Diagnosis Approach: Diagnosis relies primarily on morphology and clinical presentation, as there is no specific immunostain pattern. MFS must be differentiated from other tumors that can exhibit mixoid change (e.g., Pleomorphic Liposarcoma).