Fig. 3

Histopathological examination of biopsies taken from the lateral thorax. Interface dermatitis (a) with massive exocytosis in the epidermis of a homogenous population of lymphoid cells showing atypia (b). Clusters of neoplastic cells were present within the epidermis forming Pautrier microabscesses (c); [H&E staining, magnification × 40 (a), × 200 (b) and × 400 (c), bars = 1000 µm (a), 100 µm (b) and 10 µm (c)]. Immunohistochemical staining for CD3 showed uniform labelling of the neoplastic cells for CD3 (d), whereas staining for CD20 was negative (e). The Ki-67 labelling fraction was hard to quantify in the epidermis as the background labelling of basal epithelial cells was prominent, but by comparing the labelling fraction in the superficial dermis, it was estimated at less than 20% (f). (Magnification × 400, bar = 10 µm)