7%-81%,1, 14, 17 whereas for extrahepatic cholangiocarcinomas, the reported rates of ErbB1 expression are varied between <10% and 86%.14, 17, 18 This wide range in values for ErbB2 or ErbB1 expressed in cohorts of archival specimens of human intrahepatic or extrahepatic cholangiocarcinomas reflects

in large part a lack of standardized methodologies, as well as to other factors critically reviewed in Sirica.1 We recently reassessed several separate immunohistochemical studies Protease Inhibitor Library high throughput published between 1998 and 2005 on ErbB2 expression in archival human intrahepatic cholangiocarcinoma specimens,1 selecting those in which antigen unmasking was performed by heating of the tissue specimens in citric acid buffer (pH 6.0) and taking into account only those tumors which were scored as moderately-to-strongly Ku-0059436 mouse positive (≥2+) for plasma membrane ErbB2 immunoreactivity. From the published results of these studies, we calculated a mean frequency value of 25% ± 6% (n = 6) for intrahepatic cholangiocarcinomas exhibiting ≥ 2+ ErbB2 immunostaining.

This value is within the range of our previously published immunohistochemical findings,8 and is in line with those of more recently published studies in which the proportions of biliary tract cancers (intrahepatic, extrahepatic, and/or combined intrahepatic and extrahepatic) exhibiting moderate to strong positivity for ErbB2 immunoreactivity ranged between ∼20% and 33%.15, 17 In contrast, other recent immunohistochemical studies have yielded 2+ to 3+ ErbB2-positive immunostaining, ranging from 0.9%-4% of analyzed cases of human intrahepatic biliary tract cancers.16, 18 Reported incidences of c-erbB2 gene amplification in archival human cholangiocarcinoma specimens have also varied widely ranging from 0%-100%,1 but more recently ranged from 5%-20%, being higher in extrahepatic cholangiocarcinomas.15, 17 Our results shown in Supporting Table 2 indicate, as also reported by others15, 17 that c-erbB2 gene amplification

is relatively uncommon in human intrahepatic cholangiocarcinomas. However, as we have also now shown, cancerous epithelium of human intrahepatic Farnesyltransferase cholangiocarcinomas with high micro-optical density values for ErbB2 immunohistochemical staining intensity, can also exhibit strong immunoreactivity for phospho-ErbB2Tyr1248, regardless of whether they scored positive or negative for c-erbB2 amplification, and that constitutive phosphorylation of ErbB2 at Tyr1248, as detected by western blotting, in cultured rat (C611B) and human (HuCCT1 and TFK1) cholangiocarcinoma cell lines also occurred in the absence of c-erbB2 gene amplification. These data support the view that for most ErbB2-positive cholangiocarcinomas, ErbB2 protein overexpression when detected is more likely due to gene deregulation rather than to gene amplification.