Crypt cell carcinoma of the appendix (so-called adenocarcinoid tumor)

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Abstract
A series of 16 carcinoid tumors of the [human] appendix, including 4 examples of so-called adenocarcinoid tumors, was studied immunohistochemically for the presence of lysozyme, secretory component (SC) and IgA, within tumor cells. Stains of mucin, Paneth cells and APUD [amine and precursor uptake and decarboxylation (enterochromaffin)] cells were performed. Of the conventional carcinoid tumors, 8 showed focal tubule formation with production of PAS[periodic acid-Schiff]-positive material. In contrast to conventional carcinoids, including those showing tubule formation, adenocarcinoids contained few APUD cells and showed positive staining of tumor cells of lysozyme, SC [secretory component] and IgA. Paneth cells, staining positively for lysozyme, were present in 2 cases and mucin-containing Paneth cells were observed. A parallel study of normal small intestinal mucosa demonstrated a population of lysozyme-containing goblet cells within the crypts. Probably, so-called adenocarcinoid tumors are not derived from APUD cells but from lysozyme-producing cells of the type normally present in small intestinal crypts.