Pancreatic serous microcystic adenoma.

<p>(<b>A</b>, <b>B</b>) Formalin-fixed paraffin sections; note the clear, apparently “empty” cytoplasm of most cells in <b>A</b> (hematoxylin-eosin, 1,000x) and the poor reactivity in <b>B</b> to proteasome immunofluorescence under confocal microscopy (blue: nuclei; green: proteasome; 800x). (<b>C</b>, <b>D</b>) Semithin aldehyde-osmium fixed resin sections from the same tumour as in <b>A</b> and <b>B</b>, show abundant cytoplasmic PaCSs metachromatically stained pink with toluidine blue (<b>C</b>, 1,000x) and extensively proteasome immunofluorescent under confocal microscopy (<b>D</b>, green: proteasome; 500x). (<b>E</b>) CCEM showing proteasome immunofluorescent PaCS (5,000x); the same specimen under TEM only (<b>F</b>, 5,000x), boxed area enlarged in <b>G</b> (50,000x) shows the PaCS particulate pattern with 20S proteasome immunogold reactivity. (<b>H, I</b>) TEM of another specimen of the same tumour in <b>H</b> (5,000x), boxed area enlarged in <b>I</b> (30,000x) and further enlarged in the inset (50,000x) to show PaCS particulate ultrastructure and 19S proteasome immunogold.