Frozen section examination is still useful to establish/rule out malignancy and ascertain the status of surgical resection margins. On frozen section, tumour typing is often feasible. Enlarged non-metasta-tic lymph nodes and suspicious in situ or borderline lesions (breast nodules, polyps, ovarian cysts) are often unsuitable for frozen section procedures and require a definitive deferred diagnosis. Routine H and E staining of paraffin-embedded tissue section has to be supplemented by special stains, some of which are still used despite the advent of immunocytochemistry (ICC). Useful stains and methods are:
♦ Alcian blue cationic dye at pH 2.5 for intracytoplasmic epithelial acid mucin (e.g. mucin-producing carcinomas).
♦ Periodic acid-Schiff reaction (PAS) which visualizes glycoproteins and glycogen (e.g. Ewing's sarcoma, alveolar sarcoma, some carcinomas) and basement membranes.
♦ Romanowsky-Giemsa panoptical method for haematological proliferation.
♦ Reticulin fibre silver impregnation method.
♦ Grimelius technique for argyrophilic substances.
♦ Several stains for micro-organisms.
Most enzymes are now identified by ICC, exploiting immunogenic properties of enzymatic proteins; the majority are hydrolases, oxidases, and dehydrogenases.
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