Irish Association of Clinical Pathologists

53 cases ofmelanocytic intraepidermal neoplasia (MIN) were retrieved from theUCHG files 19901993, ranging from lentigo maligna, dysplastic naevus to florid in situ malignant melanoma. Sections were bleached in Mallory's bleach (potassium permanganate + oxalic acid) and stained with S-100 and HMB-45, with di-aminobenzene (DAB) as chromogen. Sensitivity was 100% for both stains; and HMB-45 was specific for melanocytes, while S-100 also stained sweat glands and epidermal Langerhans cells, in addition to showing increased background staining. 7/53 (13%) cases showed a subtle microinvasive component, with individual melanocytes or small nests of 2-3 cells infiltrating not more than 0.36 mm into the superficial dermis. Recurrence was zero, however, over a follow-up period of 18 months minimum, suggesting that MIN with microinvasion does not confer a worse prognosis than entirely in situ melanoma.