[49] p63 Immunohistochemical Staining Is Limited in Soft Tissue Tumors.

Vickie Y Jo, Christopher DM Fletcher. Brigham and Women's Hospital, Boston, MA

Background: p63, a p53 homolog required for epithelial development, is usually expressed in various normal epithelial tissues and epithelial malignancies. Immunohistochemical detection of p63 is used to identify myoepithelial/basal cells, confirm squamous differentiation, and in the differential diagnosis of spindle cell lesions. However, the distribution of p63 expression in mesenchymal lesions has not been characterized. We examined p63 expression in a large series of soft tissue tumors.
Design: Cases were retrieved from the authors' files. All diagnoses were based on standard and widely accepted criteria. p63 immunohistochemistry was performed using a mouse monoclonal antibody (Neomarkers, clone 4A4, Fremont, CA) at a 1:600 dilution with antigen retrieval by citrate buffer and microwave. Appropriate positive and negative controls were used. Nuclear staining was recorded as positive (diffuse, focal) or negative.
Results: 610 soft tissue tumors (whole sections) were examined for p63 expression by immunohistochemical staining. Nuclear reactivity for p63 was found in the following entities: myoepithelial carcinoma (8/20), cellular neurothekeoma (12/20), perineurioma (4/20), EWS/PNET (7/20), and diffuse-type giant cell tumor (5/20). Tumors showing infrequent, weak, or focal positivity were LGFMS (1/10), MPNST (1/20), extraskeletal myxoid chondrosarcoma (1/10), myxofibrosarcoma (1/20), epithelioid sarcoma (2/20), synovial sarcoma (1/20; glands only), embryonal RMS (1/10), DSRCT (1/10), AFX (1/20), and spindle cell melanoma (1/20). No expression of p63 was seen in all other tumor types evaluated: angiosarcoma, Kaposi sarcoma, atypical lipomatous tumor/well-differentiated liposarcoma, dedifferentiated liposarcoma, myxoid liposarcoma, spindle cell lipoma, cellular fibrous histiocytoma, DFSP, desmoid fibromatosis, nodular fasciitis, SFT, leiomyosarcoma, alveolar RMS, IMT, neurofibroma, schwannoma, so-called angiomatoid MFH, GIST, PEComa, ossifying fibromyxoid tumor, alveolar soft part sarcoma, clear cell sarcoma, follicular dendritic cell sarcoma.
Conclusions: p63 immunoreactivity is limited in soft tissue tumors, with the large majority of entities showing negative or at most focal staining. Similar to prior reports, 40% of myoepithelial carcinomas were p63-positive. Interestingly, at least weak p63 expression was observed in over 50% of cellular neurothekeomas and in a subset of cases of perineurioma, EWS/PNET, and diffuse-type giant cell tumor, the significance of which is uncertain. Absent p63 expression is typical for most soft tissue tumors, including most that would be in the differential diagnosis of spindle cell squamous carcinoma.
Category: Bone & Soft Tissue

Monday, February 28, 2011 1:00 PM

Poster Session II # 9, Monday Afternoon


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