The expression of markers for mucin-producing tumors such as Muc-2 and Muc-5AC is very heterogeneous and is observed in a wide variety of tumors, particularly those originating from the intestinal tract.5 Immunohistochemical evaluation of these specific markers to help in diagnosing carcinomas for which the primary origin is uncertain is not usually recommended. The gene discussed is MUC5AC; the disease is carcinoma.