Vascular papules in a previously irradiated breast
A 68-year-old woman was treated with breast-conserving surgery and whole-breast radiation 6 years ago. She now has three violaceous papules, each 2 to 4 mm, clustered in the irradiated skin of the upper inner quadrant. A punch biopsy of one papule shows a poorly circumscribed but small, superficial proliferation of thin-walled, irregular vascular channels lined by hobnail endothelial cells, dissecting between dermal collagen bundles; there is minimal cytologic atypia and no mitotic activity. The overlying epidermis is unremarkable. D2-40 and CD31 highlight the endothelial cells, and c-MYC immunohistochemistry is negative. FISH for MYC shows no amplification. The other two papules have not been biopsied. The patient is 6 years out from radiation and has no other skin findings.
1. How do you distinguish an atypical vascular lesion from radiation-associated angiosarcoma in this setting, and how much weight should the negative MYC FISH carry?
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Atypical vascular lesion is a small, superficial, well-circumscribed proliferation of thin-walled, branching vessels with hobnail endothelial cells dissecting dermal collagen, usually with minimal atypia and no mitoses. It arises in an irradiated field, often years after treatment. Radiation-associated angiosarcoma is infiltrative and dissecting, with cytologic atypia, endothelial multilayering, hyperchromasia, prominent nucleoli, and mitoses; it may form poorly defined channels.
MYC amplification by FISH is present in the great majority of radiation-induced angiosarcomas and is absent in atypical vascular lesions, so a positive result is a strong discriminator. A negative result, however, does not exclude angiosarcoma, particularly in early or small lesions. In this biopsy, the small size, superficiality, bland cytology, and absence of mitoses favor atypical vascular lesion, and the negative MYC supports that interpretation.
The other two papules still need sampling, because multifocality raises concern for a more extensive process and because atypical vascular lesions and angiosarcoma can coexist in an irradiated field.
2. The other two papules are biopsied and one shows dissecting vessels with endothelial multilayering, hyperchromasia, and 4 mitoses per 10 high-power fields; MYC FISH on that specimen is technically inadequate. What is your interpretation and plan?
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That specimen changes the diagnosis. Endothelial multilayering, hyperchromasia, and a mitotic rate of 4 per 10 high-power fields in a dissecting vascular proliferation in an irradiated field are features of angiosarcoma, regardless of an inadequate MYC result.
Plan:
- Interpret the findings as radiation-associated angiosarcoma and state the limitations of the failed FISH in the report.
- Repeat MYC FISH on a representative block, and add c-MYC immunohistochemistry and ERG.
- Stage with imaging of the chest wall and regional nodes, and refer urgently to a multidisciplinary sarcoma or cutaneous oncology team.
- Plan wide excision or Mohs micrographic surgery with margin control, with consideration of adjuvant radiotherapy.
The earlier bland papule does not exclude progression; angiosarcoma can arise in or near an atypical vascular lesion. The key is not to be reassured by the first negative FISH.
3. What immunohistochemical pitfalls should you keep in mind when using vascular markers in this differential?
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Pitfalls:
- D2-40 (podoplanin) labels lymphatic endothelium and is positive in both atypical vascular lesions and angiosarcoma, so it does not discriminate between them.
- CD31 and CD34 can be lost in higher-grade or epithelioid angiosarcoma, producing a falsely negative panel.
- ERG is a sensitive nuclear vascular marker but is also positive in other vascular tumors and in some carcinomas, including prostate and thyroid, so it must be interpreted in context.
- Cytokeratin can be positive in epithelioid angiosarcoma, leading to misdiagnosis as carcinoma.
- Benign reactive vascular proliferations also express these markers, so morphology, architecture, and the clinical history of radiation remain central.
- c-MYC immunohistochemistry correlates with MYC amplification but can be technically variable; a negative stain does not replace FISH when the morphology is suspicious.