Figure 6

(a) Scanning view of a "proliferative" carcinoma in-situ arising in an intra-orally transferred skin flap. The continuous linear segment indicates the surface extent of the lesion. The interrupted linear segment indicates the junction between the flap and native mucosa. Note that the carcinoma in-situ does not extend to the mucosa. The epidermal area between the arrows is not affected by in-situ carcinoma. This is attributable to irregular margins of a single lesion, being not included in the plane of the section, rather than separate lesions. The areas in rectangles labelled as b-d are magnified in Figs 6b-d respectively, so that particular features are appreciated. PA, panniculus adiposus; asterisk, submucosal minor salivary gland. (b) The linear segment indicates the junction between carcinoma in-situ and epidermis of the flap. While the surface of the carcinoma in-situ (right part of the photomicrograph) is gently mammillated and non-keratinised, the epidermis is mildly orthokeratotic (arrowhead) and shows changes similar to those in Fig. 1h. (c) The linear segment indicates the junction between carcinoma in-situ and native, parakeratinised oral mucosa. The arrow indicates artefactual crease of the section. (d) The affected epidermis shows absence of keratinisation, full-thickness severe dysplasia and elongated, variously bulbous or fused rete. Although the lower epidermal border is asymmetrical and at different levels, it is smooth and frank invasion is not seen. The increased epidermal thickness accounts for the characterisation of the carcinoma in-situ as "proliferative". Dermal inflammation is inconspicuous. The structure indicated by the arrowhead is magnified in Fig. 6e. (e) Carcinoma in-situspreads along the lining of an eccrine sweat duct ("eccrinotropism"). The paler, polymorphic and variably dyscohesive malignant keratinocytes, one of which undergoes mitosis (arrow), are easily distinguished from the more compact and densely stained normal ductal lining (arrowhead). The lumen and adluminal cuticle of the duct can be seen.