This pathology case review focuses on a challenging diagnosis: an 80-year-old male with a pink, cratered papule on the nose clinically suggestive of squamous cell carcinoma, which was pathologically revealed to be a poorly differentiated epithelial angiosarcoma. The presentation emphasizes the diagnostic pitfalls associated with partial biopsies, where solid sheets of atypical epithelioid cells with amphophilic cytoplasm can mimic carcinoma or melanoma. Key morphological features discussed include sheet-like proliferation in the dermis, ulceration, and the presence of malignant vascular channels, sometimes filled with multilayered tumor cells, leading to a "nested" appearance. Immunohistochemistry findings are highlighted, noting that while Sox10 was considered (for melanoma), the definitive diagnosis relied on finding vascular markers. The tumor showed diffuse, strong positivity for CD31 and ERG, but notably was largely negative for CD34, leading to a critical takeaway that CD34 should not be solely relied upon to rule out vascular tumors like angiosarcoma. The presenter stresses that hobnailing can occur in benign lesions, but atypical, piling-up endothelial cells forming abnormal channels are hallmarks of malignancy in this context.
00:00:08 Case Presentation: 80-year-old male with a pink, cratered papule on the nose, clinically suspected to be squamous cell carcinoma (SCC).
00:00:48 Histopathology: Dense, sheet-like proliferation of dark blue/purple epithelioid cells filling the dermis of sun-damaged skin. Ulceration and serum crust noted.
00:01:26 Diagnostic Concerns: The morphology is highly atypical, raising suspicion for SCC, melanoma (prompting Sox10), or a poorly differentiated carcinoma.
00:02:09 Pitfall of Partial Biopsy: Shallow or partial biopsies can lead to misdiagnosis, especially when strong keratin expression is present, potentially leading to a diagnosis of poorly differentiated carcinoma.
00:04:08 Key Morphological Clue: The cells exhibit a characteristic bluish-purple/slate blue-gray (amphophilic) cytoplasm.
00:04:28 Angiosarcoma Identification: The diagnosis is Epithelioid Angiosarcoma, identified by observing malignant vascular channel formation with "hobnail" endothelial cells protruding into the lumen.
00:04:56 Mimicking Nests: Multilayering of tumor cells filling vascular lumens can create a "nested" appearance that mimics nests of carcinoma.
00:05:56 Recommended IHC Panel: In cases of pleomorphic spindle cell tumors or ugly epithelial tumors (mimicking carcinoma or epithelioid sarcoma), the presenter recommends including ERG or CD31 to rule out epithelial angiosarcoma.
00:07:01 Definitive IHC Results: The tumor showed diffuse, strong expression of CD31 and ERG.
00:07:26 Critical Takeaway:CD34 was largely negative in this case, emphasizing that CD34 negativity should not be used to exclude a diagnosis of vascular tumor.
00:07:57 Hobnailing Context: While hobnailing can be benign, atypical, piling-up endothelial cells forming multi-layered channels indicate malignancy, as seen in the filling of lumens (00:08:08).
00:08:32 Growth Pattern: Angiosarcomas grow invasively by wrapping around and dividing dermal collagen and adnexal structures.
00:09:23 Clinical Importance: Angiosarcomas are aggressive tumors requiring correct identification due to unique treatment considerations.