The HER3 pathway as a potential target for inhibition in patients with biliary tract cancers

Abstract

Introduction: Expression of human epidermal growth factor receptor (HER)2 and HER3 have been investigated in small BTC studies using variable scoring systems.

Methods: HER2 and HER3 overexpression/amplification were explored following internationally agreed guidelines using immunohistochemistry (IHC) and fluorescent in-situ hybridisation (FISH), respectively. Logistic regression and survival analysis (Kaplan Meier, Log rank test and Cox Regression) were used for statistical analysis.

Results: Sixty-seven eligible patients with Stage I/II (31.3%) or III/IV (68.7%) disease at diagnosis were included. Membrane HER2 overexpression/amplification was identified in 1 patient (1%). HER3 overexpression was predominantly cytoplasmic; the rate of overexpression/amplification of HER3 in membrane and cytoplasm was 16% [ampullary cancer (AMP) (1/13; 8%), gallbladder cancer (GBC) (1/10; 10%), intra-hepatic cholangiocarcinoma (ICC) (6/26; 23%), extra-hepatic cholangiocarcinoma (ECC) (3/18; 17%)] and 24% [AMP (1/13; 8%), GBC (1/10; 10%), ICC (10/26; 38%), ECC (4/18; 22%)], respectively.

Conclusions: A significant subset of patients with BTC expressed HER3. Inhibition of HER3 warrants further investigation. A better understanding of the downstream effects of HER3 in BTC requires further mechanistic investigations to identify new biomarkers and improve patient selection for future clinical trials.

Fig 1. HER3 and HER2 expression in biliary tract cancer.

Fig 1A. and Fig 1B. show immunohistochemistry (IHC) staining demonstrating HER3 protein expression (brown, 3+ intensity) in a background of blue Haematoxylin staining to illustrate the cellular outline, Fig 1A. indicates an example of HER3 membrane expression (brown) and Fig 1B. shows an example of HER3 cytoplasmic expression (brown). Fig 1C. Shows fluorescent in situ hybridisation (FISH) to demonstrate HER3 gene amplification. Fig 1D. shows immunohistochemistry (IHC) staining demonstrating HER2 protein membrane expression (brown, 2+ intensity) in a background of blue Haematoxylin staining to illustrate the cellular outline. Fig 1E. Shows fluorescent in situ hybridisation (FISH) to demonstrate HER2 gene amplification (Ratio 2.25). HER3; human epidermal growth factor receptor 3; HER2; human epidermal growth factor receptor 2.

Fig 2. Summary of HER2 and HER3 expression and amplification in biliary tract cancer.

Fig 2A. IHC staining demonstrated that the most prevalent staining observed in this study was HER3 cytoplasmic expression. Fig 2B. FISH staining demonstrated that of the patients tested, those with intra-hepatic CC had the most amplification of HER2 and HER3, * no extra-hepatic CC patients were eligible for HER2 FISH testing. Fig 2C. Considering the combination of IHC and FISH staining together, the most prevalent combined staining observed was HER3 cytoplasmic expression, and this was predominantly in patients with intra- and extra-hepatic CC. Tables provided in each figure summarise the results of each one of the scenarios explored. Percentages (%) are calculated for Fig 2A and 2C using the total number (Tot) of such subgroup in the whole series as a denominator (ampulla: 13 patients, gallbladder: 10 patients, intrahepatic cholangiocarcinoma: 26 patients, extrahepatic cholangiocarcinoma: 13 patients); for Fig 2B, the number of patients in each subgroup undergoing FISH analysis is used as a denominator instead (Tot) (ampulla: 2 patients, gallbladder: 2 patients, intrahepatic cholangiocarcinoma: 1 patient, extrahepatic cholangiocarcinoma: 0 patients). The row “+ve” represents the number of patients from each subgroup with positive results: for Fig 2A. IHC overexpression of 3+ is considered positive; for Fig 2B, presence of amplification in FISH (labelled as “yes”) is considered positive; for Fig 2C, 3+ in IHC and/or amplification in FISH is considered as positive. CC; cholangiocarcinoma, FISH; fluorescence in-situ hybridisation, HER2 and HER3; human epidermal growth factor receptors 2 and 3, IHC; immunohistochemistry.

Fig 3. CbioPortal “in silico” analysis of data available from the genomic consortia (131 patients are included).

Fig 3A ERBB (HER) 2 & 3 analysis of CbioPortal data. Fig 3B summary of data by dataset. Fig 3C “lollipop” diagrams for ERBB 2 (green lines represent missense mutations). Fig 3D “lollipop” diagrams for ERBB 3 (green lines represent missense mutations).