Conflicts of interest exist between pharmaceutical companies that want to market their drugs, physicians that are looking for drugs that will best meet the needs of their patients, and the very ill patients that want to get better at all costs. A good predictive biomarker would be an optimal solution to these conflicts of interest. However, as experience has shown, robust, valid, sensitive, and specific biomarkers are few and far between. In the case of cetuximab, overwhelming evidence, particularly in meta-analysis studies, has shown that patients with advanced NSCLC derive benefit, especially when this antibody is combined with cytotoxic chemotherapy. Cetuximab has even been found to be of benefit after the failure of gefitinib, regardless of EGFR mutational status.93
Existing data on EGFR protein expression, evaluated through IHC, suggested that patients with high scores stand to gain when cetuximab is included in the therapy, which supports its further evaluation as a candidate biomarker. Tangible evidence, however, also exists showing that not all patients benefit. The problem with IHC is that protocols vary, which could have considerable consequences on the outcome. Even in the FLEX study, where this biomarker was evaluated, in an effort to obtain a high degree of consistency in the analysis, all the individuals involved in the interpretation of the results had to be collectively tutored.
The EGFR gene copy number detected by FISH may be another potential biomarker for the selection of NSCLC patients for treatment with EGFR-directed therapies. Patients with FISH-positive tumors have demonstrated a higher disease control rate compared to patients with FISH-negative tumors. Furthermore, survival favored FISH-positive patients receiving concurrent therapy. In the BMS099 trial, EGFR FISH positivity was seen in 54 of 104 (52%) patients, but was neither prognostic nor of predictive value with regard to cetuximab efficacy.76
Thus, EGFR FISH positivity as a predictive factor of benefit from cetuximab therapy remains undecided and needs further exploration.
It was interesting to observe that with small molecule TKIs, a preferential response was observed in females, patients with adenocarcinomas, Asians, and neversmokers.94
A more in-depth analysis of these subgroups revealed that specific activating mutations in the tyrosine kinase domain of the EGFR gene were responsible for the observed benefit from TKIs.94
In agreement with the findings in NSCLC cell line studies that these mutations were associated with sensitivity to gefitinib but not cetuximab,99
these mutations did not seem to affect patients’ response to cetuximab in the Phase III trials. In addition, no significant treatment-specific correlations between EGFR mutation status and progression free survival, overall survival, or response rate were observed in the BMS099 trial.76
Therefore, it is safe to conclude that EGFR mutations are not useful as biomarkers in cetuximab therapy.
In colorectal cancer, KRAS mutation status was found to be a useful marker of resistance because the benefit of cetuximab was found to be limited to patients with KRAS wild-type tumors.100
The results from two Phase II trials that compared platinum-based chemotherapy with cetuximab (concurrent/sequential) and with bevacizumab in patients with advanced NSCLC,88
however, showed no differences in progression-free survival or overall survival with cetuximab in relation to K-ras mutation status. The Phase III trials that evaluated K-ras mutations in NSCLC76
also found that K-ras mutation status had no impact on progression-free survival, overall survival, or response rate in relation to cetuximab administration. The observed differences between colorectal and NSCLC might be the result of alternative routes of signal transduction in NSCLC that render K-ras insignificant and impressively show that every tumor entity needs to be individually considered when establishing biomarkers for novel therapeutics. An increasing number of putative biomarkers are still in the preclinical pipeline, and it will be interesting to see which ones will be brought over into clinical trials. Thus far, the evidence of their potential use is limited to a few studies, which need to be reinforced by more groups and follow-up studies.