[531] SOX10 Expression Distinguishes Desmoplastic Melanoma from Its Histologic Mimics

Beth Palla, Albert Su, Scott Binder, Sarah Dry. UCLA, Los Angeles, CA

Background: Desmoplastic melanoma (DM) presents diagnostic challenges due to histologic mimics such as spindle cell squamous cell carcinoma, atypical fibroxanthoma (AFX) and sarcoma. While S100 usually stains DM, other melanoma markers (HMB-45, Melan-A and tyrosinase) are often negative. DM's mimics often show negative or unreliable immunohistochemical staining. SOX10 is a transcription factor that plays a role in schwannian and melanocytic cell development. The nuclear staining pattern of SOX10 transcription factor provides a clean, reliable and interpretable stain. Recently, SOX10 expression has been shown to be a very sensitive and specific marker of desmoplastic melanoma. Currently, there are no large studies comparing the sensitivity and specificity of SOX10 for desmoplastic melanoma among its most common histologic mimics.
Design: 77 cases were retrieved from the UCLA Pathology archives, including : DM (N=16), spindle cell/poorly-differentiated carcinoma (SC – N= 18), AFX (N=13), sarcoma with spindled morphology (N=20), and malignant peripheral nerve sheath tumor (MPNST – N=10). 75% (15/20) of sarcoma cases were centered in the dermis or subcutaneous tissues and included DFSP with sarcomatous transformation, myofibroblastic sarcoma, synovial sarcoma and sarcoma not otherwise specified. H&E slides were reviewed and SOX10 immunohistochemistry was performed on all cases.
Results: SOX10 was strongly, diffusely positive in 100% (16/16) of DMs and showed focal staining in 30% (3/10) of MPNSTs. All other tumors were negative for SOX10 (0% (0/18) of SCs, 0% (0/13) of AFXs, 0% (0/20) of sarcomas). SOX10 showed nuclear positivity only, as previously reported.
Conclusions: SOX10 is a sensitive marker for desmoplastic melanoma, demonstrating 100% sensitivity in this study. Importantly, SOX10 was negative in all histologic mimics that commonly occur in the dermis, including SC, AFX and sarcomas. Similar to S-100 protein, some MPNSTs show scattered positivity, but do not show diffuse positivity as in the desmoplastic melanomas. In conclusion, SOX10 is a useful marker to confirm the diagnosis of DM and to exclude its histologic mimics.
Category: Dermatopathology

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 71, Monday Morning


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