Paneth-like cells in an adenoma and adenocarcinoma in the ampulla of Vater.

A case of adenocarcinoma with significant Paneth cell differentiation arising in a villoglandular polyp at the ampulla of Vater is presented. Paneth-like cells, containing distinct fuchsinophilic granules, were a prominent component of the nonglandular invasive adenocarcinoma and were also seen in the associated adenomatous polyp. Lysozyme, trichrome, and periodic acid-Schiff digest stains, and electron microscopy confirmed that the granules were lysosomal in nature. This case confirms that cells with Paneth-like features can be a significant component in invasive neoplasms and can occur at unusual sites such as the ampulla of Vater.