EGFR inhibitors, such as cetuximab, can be successfully incorporated into combined modality regimens for the curative therapy of locally advanced SCCHN (1
). However, despite promising results, the fraction of patients benefiting from the addition of cetuximab is small, and predictors of clinical activity besides the severity of rash after treatment have not been reproducibly identified. Thus, it is important to improve patient selection and identify the patients who would benefit the most from this targeted agent. Accumulating data suggest that cetuximab may mediate immune activation as a potential mechanism of clinical activity (7
). Serum immune, angiogenic and growth factors are potentially appealing biomarkers which could be conveniently and rapidly obtained for prediction of cetuximab response.
We found low levels of VEGF and IL-6 levels measured at baseline to be consistent with better clinical outcomes. High levels of VEGF and IL-6 may be associated with poor metabolic response, as shown by residual FDG uptake on combined PET/CT, which we have previously found as an important predictor of poor PFS (13
). Since these findings may be due to false discovery we suggest investigating these serum biomarkers in future trials for selection of candidates based on pretreatment levels, or in larger studies specifically designed to validate the findings we report here. We note that a recursive partitioning model for PET response by VEGF selected a cutoff with 91% classification accuracy. However, leave-one-out cross-validation, which is more likely to generalize to other patient populations than an unvalidated model, correctly predicted the PET response of only 14 of 23 patients. This gives an accuracy of 61% with a 95% confidence interval of 41% – 81%. Thus, the conclusions regarding prognostic potential of VEGF (and IL-6) may be explained by overfitting of our models to a small dataset. Because we conducted multiple testing, we recognize that these associations may be falsely positive. Indeed, the estimated expected false discovery rate for VEGF and IL-6 and IP-10 as predictors of PET response, as based on q value, was 28%. On the other hand, these cytokines are biologically relevant for SCCHN progression, and also the results are consistent with reports from another group (18
). Byers et al reported that a panel of cytokines and angiogenic factors linked by hypoxia-associated responses, including VEGF, IL-4 and IL-8, osteopontin, growth-related oncogene-alpha, eotaxin, granulocyte-colony stimulating factor, and stromal cell-derived factor-1alpha, may correlate with outcome after induction therapy with carboplatin, paclitaxel and cetuximab, particularly in patients with HPV negative tumors (18
). The induction regimen used in our study was similar but not identical since we used cisplatin (versus carboplatin) and another taxane (docetaxel versus paclitaxel). Also, patients in our study received cetuximab during subsequent radiotherapy with concurrent cisplatin and continued cetuximab for 6 months as maintenance therapy.
In the study reported here, it was interesting that strong correlation was observed between baseline VEGF and IL-6 (p<0.001, Spearman correlation coefficient 0.817), since they are linked by the transcription factor STAT3, an oncogene and immunosuppressive marker in many cancers. IL-6 has been shown to activate STAT3, whereas STAT3 activates in turn VEGF and tumor angiogenesis (19
). However, we found no association with tumor p-STAT3 and serum markers or clinical outcome, possibly suggesting that a potential source of the VEGF and IL-6 is from circulating immune/inflammatory cells not present in the tumor microenvironment.
Recent work supports a potential immune mechanism for cetuximab clinical activity (7
), and this may be related to the serum levels of immunosuppressive cytokines, such as VEGF and IL-6 (19
). Thus, the capacity to generate an immune response and to mediate cetuximab antitumor activity may be facilitated by low baseline levels of these cytokines. Also, individual serologic growth, inflammatory, and angiogenesis markers have been correlated with disease status, including IL-1, IL-6, IL-8, GM-CSF, and VEGF; growth-regulated oncogene 1 (GRO-1); and HGF. Individually, IL-1 and IL-6 were found to promote survival and proliferation of SCC cells, and IL-8, GRO-1, VEGF, and HGF have been shown to contribute to angiogenesis, tumorigenesis, and metastasis. Furthermore, median serum concentrations of IL-6, IL-8, HGF, VEGF, and GRO-1 were found to be increased in patients with SCCHN and secreted by SCCHN cells (22
). Our group has previously shown that multiplexed analysis of a cytokine biomarker panel could be used for the development of a screening test, in heterogeneously treated SCCHN or thyroid cancer patients with active disease or no evidence of disease after 3 years from curative therapy (2
). Future studies in this area should also concentrate on repeated measurements during and after treatment, examining their associations with tumor response, relapse, complications, and survival. Because of the effect of smoking on various inflammatory mediators, we advocate more studies examining the role of biomarkers in association with smoking history which is a factor that appears to be associated with patient outcome (25
The findings of this biomarker study have several limitations which need to be addressed in future clinical trials that will prospectively evaluate a small number of biomarkers to avoid false discovery. The collection of serum and tissue was not the primary purpose of this study, sample size was rather small, and selection of the panel of biomarkers was mostly driven by the purported cell signaling network and immune effects specific to cetuximab. However, since this was not a single-agent induction regimen any effect seen could have been due to the other drugs in the regimen (i.e. docetaxel and cisplatin).
Models to predict therapeutic response to EGFR inhibitors are of major interest and have been evaluated primarily in colorectal cancer (26
). A study in patients with colorectal cancer treated with cetuximab reported longer overall survival in patients with VEGF reduction after therapy than in patients without (28
). In a small number of patients with head and neck cancer treated with the combination of erlotinib and bevacizumab, higher ratios of tumour-cell phosphorylated VEGF receptor-2 (pVEGFR2) over total VEGFR2 and endothelial-cell pEGFR over total EGFR in pretreatment biopsies were associated with tumor response (29
). Chung et al evaluated the potential value of a serum proteomic signature detected by mass spectroscopy (30
) in predicting survival after treatment with cetuximab or an EGFR tyrosine kinase inhibitor in patients with non-small cell lung cancer, colorectal cancer and SCCHN (31
). VEGF and IL-6 have been correlated with prognosis in several types of cancers, including SCCHN (19
). Whether VEGF and IL-6 are predictors of the efficacy of cetuximab-containing therapy or merely prognostic factors irrespective of treatment cannot be ascertained from our study. Our observations are hypothesis-generating and warrant validation in larger clinical studies, specifically designed to address this question. VEGF upregulation has been suggested as a mechanism of resistance to cetuximab (34
). Thus, combined targeting of VEGF with cetuximab and bevacizumab may overcome tumor resistance to cetuximab alone. Such a study could include patients with low VEGF and/or IL-6, which might be expected to enhance the rate of CR to the induction, cetuximab based regimen. Alternatively, a trial design may incorporate anti-VEGF agents, such as bevacizumab. Given the poor prognosis of patients with high VEGF levels, it is possible that the addition of anti-VEGF therapy will enhance the antitumor efficacy of TPE. We are currently testing this hypothesis in a randomized, phase II clinical trial in locally advanced SCCHN at our institution.