EGFR status is not a reliable biomarker to select patients suitable for cetuximab-based therapy

Predictive and Therapeutic Implications of a Novel PLCγ1/SHP2-Driven Mechanism of Cetuximab Resistance in Metastatic Colorectal Cancer

PURPOSE

Cetuximab is an EGFR-targeted therapy approved for the treatment of RAS wild-type (WT) metastatic colorectal cancer (mCRC). However, about 60% of these patients show innate resistance to cetuximab. To increase cetuximab efficacy, it is crucial to successfully identify responder patients, as well as to develop new therapeutic approaches to overcome cetuximab resistance.

EXPERIMENTAL DESIGN

We evaluated the value of EGFR effector phospholipase C gamma 1 (PLCγ1) in predicting cetuximab responses, by analyzing progression-free survival (PFS) of a multicentric retrospective cohort of 94 treated patients with mCRC (log-rank test and Cox regression model). Furthermore, we used in vitro and zebrafish xenotransplant models to identify and target the mechanism behind PLCγ1-mediated resistance to cetuximab.

RESULTS

In this study, levels of PLCγ1 were found increased in RAS WT tumors and were able to predict cetuximab responses in clinical samples and in vitro and in vivo models. Mechanistically, PLCγ1 expression was found to bypass cetuximab-dependent EGFR inhibition by activating ERK and AKT pathways. This novel resistance mechanism involves a noncatalytic role of PLCγ1 SH2 tandem domains in the propagation of downstream signaling via SH2-containing protein tyrosine phosphatase 2 (SHP2). Accordingly, SHP2 inhibition sensitizes PLCγ1-resistant cells to cetuximab.

CONCLUSIONS

Our discoveries reveal the potential of PLCγ1 as a predictive biomarker for cetuximab responses and suggest an alternative therapeutic approach to circumvent PLCγ1-mediated resistance to cetuximab in patients with RAS WT mCRC. In this way, this work contributes to the development of novel strategies in the medical management and treatment of patients with mCRC.

The evolving management of small bowel adenocarcinoma

BACKGROUND

Small bowel adenocarcinoma (SBA) is rare despite the fact that the small bowel represents the longest part and has the largest surface of all alimentary tract sections. Its incidence is 50-fold lower than that of colorectal carcinoma. It is often diagnosed at an advanced stage due to atypical and late symptoms, its low index of suspicion, difficult endoscopic access and poor detection by radiological imaging, resulting in impaired outcome. Due to its rarity and being molecularly a unique intestinal cancer, data regarding its optimal management are relatively sparse.

MATERIAL AND METHODS

A PubMed search was performed to identify relevant manuscripts that were recently published. Emerging data regarding the pathogenesis, the diagnosis and the treatment of SBA that resulted from recent research are discussed in this comprehensive review.

RESULTS

Genomic analysis has demonstrated that SBA is a molecularly unique intestinal cancer. Double balloon enteroscopy and capsule endoscopy are novel techniques which may result in earlier diagnosis and consequently in improvement of the generally poor prognosis. For clinically localized disease, the quality of surgery has recently been defined, with removal of at least 8-10 lymph nodes correlating with improved prognosis. Moreover, adjuvant chemotherapy seems to improve outcome of stage III disease. The combination of a fluoropyrimidine and oxaliplatin appears to be the most effective systemic chemotherapy for disseminated disease. Genomic profiling can identify potentially targetable genomic alterations in a significant proportion of SBA patients. The role of administration of targeted agents or immune checkpoint inhibitors is still unknown and subject of ongoing clinical trials. In the common case of peritoneal metastases, recent studies have shown that cytoreductive surgery and intraoperative hyperthermic intraperitoneal chemotherapy may be an attractive treatment option in selected patients.

CONCLUSIONS

SBA is a rare and unique malignancy, whose diagnostic approach and treatment are evolving, resulting in improved outcome.

The impact of co-expression of wild-type EGFR and its ligands determined by immunohistochemistry for response to treatment with cetuximab in patients with metastatic colorectal cancer

Anti-EGFR mAbs cetuximab and panitumumab are routinely used for the treatment of patients with KRAS-wild type metastatic colorectal cancer (mCRC). However, in some patients their efficacy remains modest and with no clear association between the EGFR protein expression determined by PharmDx™ kit, and response to anti-EGFR therapies. Therefore, we investigated the relative expression and predictive value of wild-type EGFR (wtEGFR), mutated EGFRvIII and EGFR ligand proteins in mCRC patients treated with cetuximab. The expression levels of wtEGFR, EGFRvIII, and EGFR ligand were determined by immunohistochemistry (IHC) in 60 tumour specimens using specific antibodies. Sections were scored according to the percentage of positive tumour cells, intensity and cellular location of staining, and these were associated with response, overall survival (OS) and progression-free survival (PFS). At cut-off value > 5%, wtEGFR, and EGFRvIII were present in 44%, and 41%, betacellulin (BTC) in 72%, followed by epigen (67%), TGFα (58%), amphiregulin (34%), EGF (31%) of the cases, respectively and 96% of the wtEGFR positive cases had co-expression of at least one ligand. We found a significant association between the expression of wtEGFR and poor response to cetuximab. In addition, the co-expression of wtEGFR with one ligand at a cut-off value of > 5% and > 10% was associated with worse response to cetuximab (P = 0.021, and P = 0.005 respectively). We found a 3-fold and 5-fold increased risk of shorter OS with expression of BTC and epigen. Interestingly, the expression of wtEGFR and its co-expression with one or two ligands was associated with shorter PFS but not with OS. The relative expression of wtEGFR and its competing ligands, which is the target for therapeutic interventions with anti-EGFR antibodies, could serve as a more reliable predictive biomarker of response to therapy with anti-EGFR mAbs in mCRC patients and warrants further investigation in large prospective studies.