Anti-EGFR Therapy for Metastatic Colorectal Cancer in the Era of Extended RAS Gene Mutational Analysis

Targeting HER2 in colorectal cancer: The landscape of amplification and short variant mutations in ERBB2 and ERBB3

BACKGROUND

In contrast to lung cancer, few precision treatments are available for colorectal cancer (CRC). One rapidly emerging treatment target in CRC is ERBB2 (human epidermal growth factor receptor 2 [HER2]). Oncogenic alterations in HER2, or its dimerization partner HER3, can underlie sensitivity to HER2-targeted therapies.

METHODS

In this study, 8887 CRC cases were evaluated by comprehensive genomic profiling for genomic alterations in 315 cancer-related genes, tumor mutational burden, and microsatellite instability. This cohort included both colonic (7599 cases; 85.5%) and rectal (1288 cases; 14.5%) adenocarcinomas.

RESULTS

A total of 569 mCRCs were positive for ERBB2 (429 cases; 4.8%) and/or ERBB3 (148 cases; 1.7%) and featured ERBB amplification, short variant alterations, or a combination of the 2. High tumor mutational burden (≥20 mutations/Mb) was significantly more common in ERBB-mutated samples, and ERBB3-mutated CRCs were significantly more likely to have high microsatellite instability (P<.002). Alterations affecting KRAS (27.3%) were significantly underrepresented in ERBB2-amplified samples compared with wild-type CRC samples (51.8%), and ERBB2- or ERBB3-mutated samples (49.0% and 60.8%, respectively) (P<.01). Other significant differences in mutation frequency were observed for genes in the PI3K/MTOR and mismatch repair pathways.

CONCLUSIONS

Although observed less often than in breast or upper gastrointestinal carcinomas, indications for which anti-HER2 therapies are approved, the percentage of CRC with ERBB genomic alterations is significant. Importantly, 32% of ERBB2-positive CRCs harbor short variant alterations that are undetectable by routine immunohistochemistry or fluorescence in situ hybridization testing. The success of anti-HER2 therapies in ongoing clinical trials is a promising development for patients with CRC. Cancer 2018;124:1358-73. © 2018 Foundation Medicine, Inc. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society.

Autocrine expression of the epidermal growth factor receptor ligand heparin-binding EGF-like growth factor in cervical cancer

In cervical cancer, the epidermal growth factor receptor (EGFR) is overexpressed in 70–90% of the cases and has been associated with poor prognosis. EGFR-based therapy is currently being explored in cervical cancer. We investigated which EGFR ligand is primarily expressed in cervical cancer and which cell type functions as the major source of this ligand. We hypothesized that macrophages are the main source of EGFR ligands and that a paracrine loop between tumor cells and macrophages is responsible for ligand expression. mRNA expression analysis was performed on 32 cervical cancer cases to determine the expression of the EGFR ligands amphiregulin, β-cellulin, epidermal growth factor (EGF), epiregulin, heparinbinding EGF-like growth factor (HB-EGF) and transforming growth factor α (TGFα). Subsequently, protein expression was determined immunohistochemically on 36 additional cases. To assess whether macrophages are the major source of EGFR ligands, immunohistochemical double staining was performed on four representative tissue slides. Expression of the chemokines granulocyte-macrophage colony-stimulating factor (GM-CSF) and C-C motif ligand 2 (CCL2) was determined by mRNA in situ hybridization. Of the known EGFR ligands, HB-EGF had the highest mRNA expression and HB-EGF and EGFR protein expression were highly correlated. Tumor specimens with high EGFR expression showed higher numbers of macrophages, and higher expression of GM-CSF and CCL2, but only a small subset (9%) of macrophages was found to be HB-EGF-positive. Strikingly, 78% of cervical cancer specimens were found to express HB-EGF. Standardized assessment of staining intensity, using spectral imaging analysis, showed that HB-EGF expression was higher in the tumor compartment than in the stromal compartment. These results suggest that HB-EGF is an important EGFR ligand in cervical cancer and that cervical cancer cells are the predominant source of HB-EGF. Therefore, we propose an autocrine EGFR stimulation model in cervical carcinomas.

Approaches for Identifying Novel Targets in Precision Medicine: Lessons from DNA Repair

Genome stability is maintained by a number of elegant mechanisms, which sense and repair damaged DNA. Germline defects that compromise genomic integrity result in cancer predisposition, exemplified by rare syndromes caused by mutations in certain DNA repair genes. These individuals often exhibit other symptoms including progeria and neurodegeneration. Paradoxically, some of these deleterious genetic alterations provide novel therapeutic opportunities to target cancer cells; an excellent example of such an approach being the recent development of poly (ADP-ribose) polymerase inhibitors as the first 'synthetic lethal' medicine for patients with BRCA-mutant cancers. The therapeutic exploitation of synthetic lethal interactions has enabled a novel approach to personalised medicine based on continued molecular profiling of patient and tumour material. This profiling may also aid clinicians in the identification of specific drug resistance mechanisms following relapse, and enable appropriate modification of the therapeutic regimen. This chapter focuses on therapeutic strategies designed to target aspects of the DNA damage response, and examines emerging themes demonstrating mechanistic overlap between DNA repair and neurodegeneration.