Photomicrographs of features of islet α-cell carcinoma, (a) in the bottom right, part of an adjacent well-circumscribed adenoma showing characteristic ribbon-like growth of well-differentiated, hyperchromatic cells around blood-filled spaces contrast with the appearance of the carcinoma which presents solid sheets and nests of more basophilic, anaplastic cells. The locally invasive growth of the carcinoma between exocrine tissue elements and serosal spread (arrows) illustrates the characteristic features of such tumours, (haematoxylin and eosin) (b) GLP-1 immunostaining of a semiserial section of the tumours shown in (a) illustrating the distinction between characteristics of different tumours and the local serosal carcinoma spread (arrows), (c) part of same carcinoma shown in (a) illustrating the breakdown of ordered hyperchromatic adenomatous tumour structure (arrow) to well-defined, monomorphic anaplastic cell appearances within solid nests/sheets, (d) increased magnification of part of a carcinoma developed from within an adenoma indicating the differences in appearance between the well-ordered, hyperchromatic adenoma cells intermixed with basophilic, more haphazard arrangement of anaplastic carcinoma cells showing several mitotic figures (arrows) and growing in small nests, apparently derived from the bases of the ribbons of hyperchromatic cells, (e) increased magnification of solid nests and sheets of anaplastic, basophilic cells derived from bases of hyperchromatic cell ribbons resulting in fragmentation of these latter, (f) part of carcinoma shown in (a) showing tumour pleiomorphism illustrated by separation into two polymorphic cohorts defined by characteristic cellular and nuclear size, (g) part of locally invasive carcinoma shown in (a) illustrating low incidences of mitotic figures (arrows) and apoptotic bodies (arrowheads), (h) insulin-immunostained carcinoma shown in (a) illustrating single cells and clusters of β-cells of normal appearance. (a, c–g, haematoxylin and eosin). (Objective lens magnifications: a ×5; b, d ×10; c, e, f, h ×20; g ×40).