Dimorphic immunohistochemical staining in ocular sebaceous neoplasms: A useful diagnostic aid

We studied whether patterns of immunostaining in formalin-fixed, paraffin-embedded tissue could help to distinguish between sebaceous neoplasms of the eyelid and other eyelid neoplasms. We applied antibodies to human milk fat globule-1 (HMFG1), cytokeratins (PKK1 and MNF116), epithelial membrane antigen (EMA) and carcino-embryonic antigen (CEA) to normal eyelid tissue and to a range of sebaceous lesions of the eyelid; these included sebaceous hyperplasia, sebaceous adenoma and sebaceous epithelioma, in addition to well to poorly differentiated sebaceous carcinoma. The central and peripheral cellular components of normal sebaceous glands and neoplastic sebaceous lesions showed a distinctive dimorphic staining pattern with the antibody panel used. The central foamy 'sebaceous' cells expressed HMFG1 and EMA, but not PKK1 or MNF116, whereas the smaller, peripheral basal and ductal cells expressed PKK1 or MNF116 but not HMFG1 or EMA. CEA expression in sebaceous cells was unhelpful diagnostically. Normal sebaceous glands and all sebaceous neoplasms show a dimorphic cell population that can be identified using a small panel of antibodies on formalin-fixed, paraffin-embedded tissue. This distinctive staining pattern can be assessed retrospectively, even in small biopsies, and largely removes the need for fat stains on frozen sections to differentiate sebaceous lesions from other ocular neoplasms. The results also support the suggestion that ocular sebaceous neoplasms arise from a common stem cell, rather than from either sebaceous or basal/ductal cells.