This video details the histological examination of a skin nodule excised from the thigh of a 70-year-old woman, leading to the diagnosis of Myxofibrosarcoma (MFS). The tumor presents as a hypocellular, bluish-myxoid nodule in the deep dermis and subcutis, characterized by significant cellular atypia (hyperchromatic, pleomorphic, multi-nucleated cells) set within a myxoid background. Based on low cellularity, the tumor is classified as Grade 1 MFS. The speaker emphasizes the importance of recognizing MFS, noting it is a relatively common sarcoma that frequently involves superficial soft tissue (dermis/subcutis) in older adults. Crucially, MFS is highly infiltrative, with tumor cells tracking along fibrous septa far beyond the main mass, often resulting in challenging positive surgical margins and a high risk of local recurrence.
Summarizing the Transcript: Myxofibrosarcoma (Grade 1)
0:11 Case Presentation: The specimen is a large excision of a skin nodule from the thigh of a 70-year-old woman, extending down to the fascia.
0:23 Initial Findings: A bluish, myxoid nodule is present in the deep dermis and subcutis. An important finding is the presence of abnormally thick fibrous septa between the fat lobules, which are typically thin and delicate.
0:51 Histological Features: Although hypocellular and myxoid (initially suggesting a benign myxoma), closer examination reveals distinct atypia. Cells are hyperchromatic, pleomorphic, and scattered, with some being multi-nucleated.
1:40 Diagnosis: This presentation (mixoid tumor with atypical cells, infiltrating the subcutis/dermis of an elderly patient’s extremity) is a classic example of Myxofibrosarcoma (MFS).
2:00 Grading: Due to the very low cellularity observed, this is classified as a Grade 1 (low-grade) Myxofibrosarcoma. The speaker intentionally uses "Myxofibrosarcoma Grade 1" to avoid confusion with Low-Grade Fibromyxoid Sarcoma (2:11).
2:35 Epidemiology and Location: MFS is one of the more common forms of sarcoma, seen regularly by the pathologist. It typically affects older adults and is most common on the extremities.
3:00 Clinical Significance for Dermatopathologists: MFS often arises above the deep fascia, involving the dermis and subcutis, and can be clinically misdiagnosed as a benign cyst or skin bump.
4:04 Key Takeaway – Infiltrative Nature: MFS is notoriously infiltrative. Tumor cells "ooze" out of the main nodules and trickle along the fibrous septa, often extending far beyond the visible or palpable mass, making wide surgical margins difficult to achieve (4:45).
5:01 Impact on Surgery: The highly infiltrative growth pattern often leads to positive margins, resulting in a high chance of local recurrence. Unlike many other sarcomas, which are well-circumscribed, MFS is rarely encapsulated (5:18).
6:04 Ancillary Studies: MFS is primarily an H&E (histological) diagnosis. Immunostains (like S100) are typically used only to rule out other rare entities (e.g., myxoid melanoma). MFS has random chromosomal abnormalities and lacks specific molecular or immunohistochemical markers (6:49).