EGFRvIII: An Oncogene with Ambiguous Role

Epidermal growth factor receptor variant III (EGFR^vIII) seems to constitute the perfect therapeutic target for glioblastoma (GB), as it is specifically present on up to 28–30% of GB cells. In case of other tumor types, expression and possible role of this oncogene still remain controversial. In spite of EGFR^vIII mechanism of action being crucial for the design of small active anticancer molecules and immunotherapies, i.e., CAR-T technology, it is yet to be precisely defined. EGFR^vIII is known to be resistant to degradation, but it is still unclear whether it heterodimerizes with EGF-activated wild-type EGFR (EGFR^WT) or homodimerizes (including covalent homodimerization). Constitutive kinase activity of this mutated receptor is relatively low, and some researchers even claim that a nuclear, but not a membrane function, is crucial for its activity. Based on the analyses of recurrent tumors that are often lacking EGFR^vIII expression despite its initial presence in corresponding primary foci, this oncogene is suggested to play a marginal role during later stages of carcinogenesis, while even in primary tumors EGFR^vIII expression is detected only in a small percentage of tumor cells, undermining the rationality of EGFR^vIII-targeting therapies. On the other hand, EGFR^vIII-positive cells are resistant to apoptosis, more invasive, and characterized with enhanced proliferation rate. Moreover, expression of this oncogenic receptor was also postulated to be a marker of cancer stem cells. Opinions regarding the role that EGFR^vIII plays in tumorigenesis and for tumor aggressiveness are clearly contradictory and, therefore, it is crucial not only to determine its mechanism of action, but also to unambiguously define its role at early and advanced cancer stages.

Localized BCNU chemotherapy and the multimodal management of malignant glioma

BACKGROUND

Gliomas account for 42% of all primary CNS neoplasms and 77% of all malignant primary CNS neoplasms. Unfortunately the high-grade variant of gliomas, glioblastoma multiforme (GBM), is difficult to treat and generally considered incurable. Survival rates are generally poor, and neurological morbidity in the setting of disease progression is high. Fortunately, significant progress has been achieved in the past decade in our understanding of the molecular biology of this aggressive tumour histology and, as a consequence, there is renewed clinical trial activity in this area focused on improving quality of life, treatment-related morbidity and outcomes.

METHODS

A review of literature from June 2005 to June 2008 was conducted on multimodal treatment of malignant glioma (MG) patients, using specific search criteria in Medline, EMBASE, and BIOSIS. Abstracts from relevant US and European medical (cancer) meetings were also evaluated.

RESULTS

The established therapies for MG include surgery, radiotherapy (RT), and local or systemic chemotherapy. However, over the last 10 years only two chemotherapeutic agents have received regulatory approval for treatment of MG: polifeprosan 20 with carmustine (BCNU implant) and temozolomide (TMZ), an imidazotetrazine derivative of dacarbazine. More recent advances in the treatment of brain tumours have been in the development of multimodal approaches. Specific interest in the combination of BCNU implant and TMZ has arisen due to the demonstrable depletion by TMZ of the DNA repair enzyme responsible for resistance to a nitrosourea such as BCNU. Further interest in this combination stems from the observation that there is a difference in the time to peak effect for each agent. Additional emerging data suggest that multimodal therapy with maximal resection and BCNU implants, followed by adjuvant therapy with radiation and TMZ, is effective and well-tolerated in patients with initial high-grade, resectable MG.

CONCLUSIONS

The increasing body of efficacy data suggests that this combination of BCNU implants and TMZ within a multimodal treatment strategy including surgery and RT may provide an enhanced benefit compared with the use of either of these agents alone in select patients with high-grade glioma.