[48] CD1a Immunopositivity in Perivascular Epithelioid Cell Neoplasms (PEComas): True CD1a Expression or Technical Artifact?

WA Ahrens, AL Folpe. Carolinas Medical Center, Charlotte, NC; Mayo Clinic, Rochester, MN

Background: PEComas comprise a family of rare neoplasms composed of morphologically distinctive perivascular epithelioid cells exhibiting a “myomelanocytic” immunophenotype. The distinction of PEComas from other tumors with melanocytic and smooth muscle differentiation can be difficult. A recent study has claimed that PEComas routinely express CD1a, a Langerhans cell-associated transmembrane glycoprotein involved in antigen presentation, and that expression of this marker may be helpful in the distinction of PEComas from various mimics. We evaluated a series of PEComas and potential mimics for CD1a expression.
Design: A total of 54 cases (27 PEComas; 11 leiomyosarcomas; 10 melanomas; 6 clear cell sarcomas) were evaluated in 2 laboratories (Laboratory A: 31 cases, Laboratory B 23 cases). Nine Laboratory B cases were retested at Laboratory A. Laboratory A methods: MTB1 clone (1:20, Novocastra), heat-induced epitope retrieval in EDTA (pH 8.0), Dako Advance detection system (Dako Corp.) with background reducing diluent. Laboratory B methods: MTB1 clone (1:30, CellMarque), heat-induced epitope retrieval in Medium Cell Conditioner #1 (pH 8.0–9.0), streptavidin-biotin detection system with DAB chromogen. Scoring: 1+, 5-25%; 2+, 26-50; 3+, >51%. Langerhans cells served as a positive internal control in all tested cases.
Results: All Laboratory A cases were negative. 16 Laboratory B PEComas (14 renal angiomyolipomas, 1 soft tissue PEComa, 1 pulmonary clear cell "sugar" tumor) showed CD1a immunopositivity (1+: 7 cases; 2+: 7 cases; 3+: 2 cases). All non-PEComas were negative. All positive PEComas showed cytoplasmic staining only, without membranous staining. The 9 Laboratory B positive PEComas were negative when retested at Laboratory A.
Conclusions: We conclude that PEComas do not truly express CD1a in a biologically plausible membranous pattern, but may instead show aberrant cytoplasmic immunopositivity in some laboratories. Close inspection of published photomicrographs of previously reported CD1a-positive PEComas shows an identical pattern of cytoplasmic positivity. This aberrant pattern of immunopositivity likely reflects a technical artifact related to epitope retrieval and detection methods. Alternatively, this staining could represent cross-reactivity with an epitope unique to PEComas, as it was not observed in non-PEComas. Ultimately, however, we do not believe there is a real role for CD1a immunohistochemistry in the differential diagnosis of PEComas.
Category: Bone & Soft Tissue

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 7, Tuesday Morning

 

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