This pathology case review focuses on a slow-growing hand mass in a 24-year-old, leading to the diagnosis of Epithelioid Sarcoma. The discussion highlights the classic presentation of this rare but aggressive tumor—a nodular mass on the distal extremity of a young adult, often featuring central necrosis. Histologically, the tumor cells are large and epithelioid, exhibiting dense pink cytoplasm (keratin-positive) and atypical nuclei with pale chromatin. Crucially, the tumor is characterized by the immunohistochemical loss of the INI1 (SMARCB1) protein. Due to the necrobiotic pattern, pathologists are cautioned to include Epithelioid Sarcoma in the differential diagnosis of deep granuloma annulare and rheumatoid nodules, as it can be a challenging microscopic mimic.
Epithelioid Sarcoma: Pathology Case Review
0:00 Case Presentation: A 24-year-old patient presents with a slow-growing, large, multi-nodular mass located in the hand (distal extremity).
1:03 Confirmed Diagnosis: The mass is confirmed to be an Epithelioid Sarcoma.
1:17 Classic Presentation: This tumor typically presents as a mass on the distal extremity (hand/foot) of a young adult, often making deep nodules near the subcutis or fascia.
1:30 Histology and Mimics: The nodules commonly exhibit central necrosis, which can cause them to mimic benign palisaded necrobiotic granulomas, such as rheumatoid nodules or deep granuloma annulare.
2:06 Cytology: The cells are large, atypical, and highly cellular with mitotic activity. They feature dense pink cytoplasm (due to an abundance of keratin filaments) and pale, vesicular chromatin, giving them an epithelioid appearance.
3:27 Molecular Marker (INI1 Loss): The vast majority of these tumors show characteristic loss of expression of the tumor suppressor gene product INI1 (SMARCB1) via immunohistochemistry (IHC). Background inflammatory and endothelial cells retain INI1 staining, serving as a vital internal control.
4:19 Aggressive Behavior: Epithelioid sarcoma is a relatively aggressive tumor known to metastasize to lymph nodes and spread up the extremity (sporotrichoid pattern), breaking traditional rules for sarcomas.
5:14 Key Takeaway: Pathologists should always include Epithelioid Sarcoma in the differential diagnosis when considering rheumatoid nodule or deep granuloma annulare, as it can closely mimic these far more common benign conditions.