Is the Anti-S-100 Antibody Decreasing Its Affinity for Epidermal Melanocytes? A Possible Diagnostic Pitfall.
Felipe J Solano, Jyoti Kapil, Michael T Deavers, Michael S McLemore, Victor G Prieto. University of Texas Health Science Center at San Antonio; George Washington University Medical Center, Washington, DC; University of Texas M.D. Anderson Cancer Center, Houston
Background: Immunohistochemical (IHC) staining with anti-S-100 is used as a reliable marker of melanocytic differentiation. At MD Anderson Cancer Center (MDACC), IHC technique employs a monoclonal antibody derived from murine species stimulated with the purified bovine S-100 protein immunogen (clone 15E2E2), used in a 1:900 dilution to stain paraffin-embedded tissue following a standard protocol. Based on our experience at MDACC, anti-S-100 IHC frequently fails to label epidermal melanocytes while strongly labeling epidermal and dermal dendritic cells and nerves. Our objective is to determine whether epidermal melanocytic staining affinity with anti-S-100 is preserved in dermatopathology cases.
Design: We searched the Pathology files at MDACC for recent inside and outside consultation cases in dermatopathology in which anti-S-100 IHC was performed and available for review. Epidermal melanocytes labeling with anti-S100 were evaluated in each case for intensity (0: negative, 1: weak, 2: moderate to marked), and for percentage of cells staining (0: negative, 1: 1-25%, 2: 26-75%, 3: >75 %). For one outside case, anti-S-100 IHC was repeated, and for another, the anti-S-100 was performed in-house.
Results: From 3/1/2010 to 9/24/2010, 28 skin cases (18 inside, 10 outside cases) were identified (see Table 1). All cases had squamous epithelium with normal melanocytes, as well as dermal dendritic cells and nerves to serve as an internal positive control. In a majority of cases, additional IHC had previously been performed which highlighted melanocytes (i.e., anti-MART1, HMB45, anti-tyrosinase, or MITF).
|Intensity/Percentage of Staining with Anti-S-100:||0/0||1/1||2/1||1/2||2/2||2/3|
|Number of Inside Cases:||4||9||2||1||3||1|
|Number of Outside Cases:||1||4||0||1||1||2|