[528] MITF Is the Most Effective Melanocytic Marker for Evaluation of Atypical Intraepidermal Melanocytic Proliferations

Grant E Nybakken, Michael Sargen, Ronnie Abraham, Xiaowei Xu. Hospital of the University of Pennsylvania, Philadelphia, PA

Background: Atypical intraepidermal melanocytic proliferations (AIMP) are lesions along the spectrum between actinic lentigo and melanoma in situ. They are non-nested, pagetoid and/or lentiginous melanocytic proliferations for which a definitive diagnosis is difficult to provide. Immunohistochemistry for S-100, MITF and Melan A is commonly used to aid differentiation of these entities. However, we have noticed that Melan-A, MITF and S-100 all appear to stain different numbers of cells in the epidermis. We attempt to determine the best IHC stains for evaluation of epidermal melanocytes.
Design: 49 specimens with a diagnosis of AIMP were selected from historical archives. Appropriate formalin fixed paraffin embedded blocks containing representative lesional tissue were cut and immunohistochemically stained with S-100, Melan A and MITF. A representative area of AIMP was selected on H&E and the fraction of cells at the dermal-epidermal junction that are melanocytes was evaluated. The results were independently determined by three pathologists.
Results: S-100 and Melan-A demonstrate cytoplasmic staining and MITF demonstrates nuclear staining. Melan-A stains a significantly higher percentage of cells at the dermal epidermal junction (mean 55% of cells were positive) than any other stain. MITF stains 34% of the cells near the dermal epidermal junction, which is similar to the percentage of melanocytes identified by H&E. S-100 stains the fewest number of cells (mean 9%). The difference between MITF and H&E is not statistically significant. Melan-A stains the highest percentage of cells in 47 of the 49 specimens evaluated.
Conclusions: Different immunohistochemical stains are liable to produce distinct estimates of the number and confluence of melanocytes at the dermal-epidermal junction. Due to the cytoplasmic staining pattern of Melan A, junctional melanocytes may often be overinterpreted. S100 staining, although cytoplasmic, is often weak and patchy. MITF produces results that most closely approximate those of H&E. Therefore, MITF is an effective stain for detecting melanocytes in AIMP, and should be preferentially used for evaluation of these lesions.
Category: Dermatopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 114, Wednesday Afternoon


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