Hamartomatous solitary polyp with malignant progression in the jejunum. A histochemical and immunohistochemical study by light and electron microscopy.

A case of solitary hamartomatous jejunal polyp with adenomatous and carcinomatous changes in a 16-year-old girl is reported. In the hamartomatous polyp, neutral and acid non-sulfate mucosubstance was detected, principally in goblet cells; carcinoembryonic antigen was demonstrated on the surfaces of the microvilli and luminal border of the crypts and glands; absorptive columnar, goblet, argentaffin, argyrophil and Paneth cells were evident. The adenomatous and, mainly, the carcinomatous areas revealed a decreased amount of mucosubstance and a variable degree of positive intracytoplasmic staining for carcinoembryonic antigen. With electron microscopy, the adenomatous areas showed columnar absorptive cells and mucus-secreting goblet cells; also immature columnar cells were observed in the dysplastic zones. To our knowledge, this is the first study to document the histochemical, immunohistochemical and ultrastructural features of a hamartomatous polyp with neoplastic transformation.