Cytokeratins 7, 17, and 20 reactivity in pancreatic and ampulla of vater adenocarcinomas - Percentage of positivity and distribution is affected by the cut-point threshold

We studied reactivity of cytokeratins (CK) 7, 17, and 20 in 64 pancreaticob iliary adenocarcinomas to examine the effect of different cut-point thresho lds on "positive" results, compare ampulla of Vater and pancreas adenocarci nomas, and provide additional experience with CK17 reactivity. Almost all n eoplasms had extensive CK7 reactivity. The number of CK20-positive cases de creased from 29 (45%; any stained cells) to 19 (30%; > 25% staining) to 14 (22%; > 50% staining) with an increasing threshold of reactive cells. Simil ar shifts in the distribution of CK7 and CK20 reactivity occurred when diff erent thresholds of reactivity were used for a positive result. There were no differences in CK7 and CK20 reactivity in pancreas only, ampulla only, a nd neoplasms involving both sides. Of 64 adenocarcinomas, 29 (45%) had no o r single-cell CK17 reactivity, and 19 (30%) had reactivity in more than 50% of neoplastic cells. Ampulla of Vater and pancreas adenocarcinomas have si milar CK immunophenotypes that cannot assist in distinguishing ampullary fr om pancreatic neoplasms on endoscopically procured tissue. CK17 staining oc curs in approximately 50% of pancreaticobiliary adenocarcinomas and is usua lly patchy. Single antibody staining results, especially CK7 and CK20 coord inate reactivity, are influenced by the reactivity threshold used.