Clairvoyance or reliable prediction of the future?

Abstract

The first reports showing that the epidermal growth factor receptor (EGFR) is expressed in non-small-cell lung cancer (NSCLC) appeared two decades ago [1.Veale D. Ashcroft T. March C. et al.Characterization of epidermal growth factor receptors in non-small cell lung cancer.Br J Cancer. 1987; 55: 513-516Crossref PubMed Scopus (278) Google Scholar]. This has led to many attempts to interact with EGFR signaling, but it was not until some 4 years ago that the first positive experiences with gefitinib and erlotinib in patients with recurrent NSCLC were reported [2.Kris M.G. Natale R.B. Herbst R.S. et al.Efficacy of gefitinib, an inhibitor of the epidermal growth factor receptor tyrosine kinase, in symptomatic patients with non-small cell lung cancer.JAMA. 2003; 290: 2149-2158Crossref PubMed Scopus (2494) Google Scholar, 3.Fukuoka M. Yano S. Giaccone G. et al.Multi-institutional randomized phase II trial of gefitinib for previously treated patients with advanced non-small cell lung cancer.J Clin Oncol. 2003; 21: 2237-2246Crossref PubMed Scopus (2869) Google Scholar, 4.Peréz-Soler R. Chachoua A. Hammond L.A. et al.Determinants of tumor response and survival with erlotinib in patients with non-small-cell lung cancer.J Clin Oncol. 2004; 22: 3238-3247Crossref PubMed Scopus (1046) Google Scholar]. Treatment with both of these small molecules, that inhibit the tyrosine kinase domain of the EGFR (EGFR TKIs), has been marked by favorable clinical responses in distinct groups of NSCLC patients. Clearly never smokers, patients from Asian origin, patients with adenocarcinoma or bronchioloalveolar carcinoma and female gender experienced the greatest benefit from treatment with EGFR TKIs and these observations made by different groups of investigators [3.Fukuoka M. Yano S. Giaccone G. et al.Multi-institutional randomized phase II trial of gefitinib for previously treated patients with advanced non-small cell lung cancer.J Clin Oncol. 2003; 21: 2237-2246Crossref PubMed Scopus (2869) Google Scholar, 4.Peréz-Soler R. Chachoua A. Hammond L.A. et al.Determinants of tumor response and survival with erlotinib in patients with non-small-cell lung cancer.J Clin Oncol. 2004; 22: 3238-3247Crossref PubMed Scopus (1046) Google Scholar, 5.Miller V.A. Kris M.G. Shah N. et al.Bronchioloalveolar pathologic subtype and smoking history predict sensitivity to gefitinib in advanced non-small-cell lung cancer.J Clin Oncol. 2004; 22: 1103-1109Crossref PubMed Scopus (723) Google Scholar, 6.Haringhuizen A. van Tinteren H. Vaessen H.F. et al.Gefitinib as a last treatment option for non-small-cell lung cancer: durable disease control in a subset of patients.Ann Oncol. 2004; 15: 786-792Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar, 7.Shepherd F. Pereira J. Ciuleanu T.E. et al.Erlotinib in previously treated non-small-cell lung cancer.N Engl J Med. 2005; 353: 123-132Crossref PubMed Scopus (5100) Google Scholar] have induced intensive research efforts to identify biomarkers, that may predict which patient will favorably respond to this type of medication. Three years ago EGFR mutations were discovered in patients with dramatic responses to EGFR TKIs [8.Lynch T.J. Bell D.W. Sordella R. et al.Activating mutations in the epidermal growth factor receptor underlying responsiveness of non-small-cell lung cancer to gefitinib.N Engl J Med. 2004; 350: 2129-2139Crossref PubMed Scopus (10043) Google Scholar, 9.Paez J.G. Janne P.A. Lee J.C. et al.EGFR mutations in lung cancer: correlation with clinical response to gefitinib therapy.Science. 2004; 304: 1497-1500Crossref PubMed Scopus (8497) Google Scholar, 10.Pao W. Miller V. Zakowski M. et al.EGF receptor gene mutations are common in lung cancers from ‘never smokers’ and are associated with sensitivity of tumors to gefitinib and erlotinib.Proc Natl Acad Sci USA. 2004; 101: 13306-13311Crossref PubMed Scopus (3891) Google Scholar]. These mutations in the EGFR kinase domain are generally referred to as activating mutations since they appear to result in enhanced kinase activity of the receptor, thereby providing an explanation for increased responsiveness to EGFR TKIs [11.Kosaka T. Yatabe Y. Endoh et al.Mutations of the epidermal growth factor gene in lung cancer: biological and clinical implications.Cancer Res. 2004; 64: 8919-8923Crossref PubMed Scopus (1131) Google Scholar]. Shortly thereafter, amplification of wild-type EGFR and alterations in other ErbB family members were also reported to be associated with responses to EGFR TKIs [12.Cappuzzo F. Varella-Garcia M. Shigematsu H. et al.Increased HER2 gene copy number is associated with response to gefitinib therapy in epidermal growth factor receptor-positive non-small-cell lung cancer patients.J Clin Oncol. 2005; 23: 5007-5018Crossref PubMed Scopus (345) Google Scholar, 13.Hirsch F. Varella-Garcia M. McCoy J. et al.Increased epidermal growth factor receptor gene copy number detected by fluorescence in situ hybridization associates with increased sensitivity to gefitinib in patients with bronchioloalveolar carcinoma subtypes: a Southwest Oncology Group Study.J Clin Oncol. 2005; 23: 6838-6845Crossref PubMed Scopus (554) Google Scholar]. It is important to note that all these observations were done in retrospect in selected groups of patients and thus confirmatory and preferably prospective studies are needed. Furthermore, a separation between the prognostic and predictive importance of markers is considered important [14.Shepherd F.A. Tsao M.-S. Unraveling the mystery of prognostic and predictive factors in epidermal growth factor receptor therapy.J Clin Oncol. 2006; 24: 1219-1221Crossref PubMed Scopus (90) Google Scholar]. Prognostic markers ideally predict survival independent from the treatment administered, while predictive markers forecast tumor shrinkage and/or prolonged survival due to a specific treatment. The interpretation of the literature is becoming difficult if we consider the inevitable constraints of biomarker studies. The most important issue is the availability of representative tumor material. Representative tumor material from the two large randomized studies evaluating erlotinib and gefitinib (BR 21 and the ISEL) could be retrieved in a minority of cases only [15.Tsao M.S. Sakurada A. Cutz J.C. et al.Erlotinib in lung cancer—molecular and clinical predictors of outcome.N Engl J Med. 2005; 353: 133-144Crossref PubMed Scopus (1738) Google Scholar, 16.Hirsch F.R. Varella-Garcia M. Bunn P.A. et al.Molecular predictors of outcome with gefitinib in a phase III placebo-controlled study in advanced non-small-cell lung cancer.J Clin Oncol. 2006; 24: 5034-5042Crossref PubMed Scopus (688) Google Scholar]. Also the outcome of laboratory tests must be carefully weighted. This is especially true for DNA-based tests, including PCR-based tests, where the relative proportion of tumor cells and normal cells will influence the outcome. The presence of mutations in the EGFR domain are usually assessed after PCR amplification of DNA isolated from the tumor and the divergent results reported might be attributable to low quantities of representative tumor material, which is a reality with biopsies taken through the bronchoscope. For the determination of EGFR overexpression and gene amplification, various techniques are available including immunohistochemistry (IHC), FISH and quantitative PCR. Divergent results obtained by these techniques might also be related to differences in methodology. It still remains to be determined what the exact frequency is of high-level EGFR gene amplification, low-level EGFR gene amplification and the association of these amplification events with increased expression of EGFR protein. In addition, it remains to be established to what extent the combination of EGFR mutations with EGFR amplification/overexpression affects response to TKI therapy. In this issue, Dziadziuszko et al. [17.Dziadziuszko R. Holm B. Skov B.G. et al.Epidermal growth factor receptor gene copy number and protein level are not associated with outcome of non-small cell lung cancer patients treated with chemotherapy.Ann Oncol. 2007; 18: 447-542Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar] of the University of Colorado Cancer Center add an important piece of information to the relationship between EGFR gene copy number and EGFR IHC and the outcome after chemotherapy treatment of NSCLC patients. Increased EGFR copy numbers were associated with increased expression of EGFR protein; but neither was associated with response to chemotherapy or survival. Together with the reports revealing a correlation between EGFR copy number and IHC and EGFR TKI response, this result is forming the argument to consider EGFR copy number and IHC as specific predictors of the outcome of treatment with EGFR TKIs. Is there sufficient evidence to conclude that EGFR copy numbers and overexpression are predictive markers for response to EGFR TKIs? The results obtained by (retrospectively) analyzing tumor material from patients treated in randomized studies may appear convincing, but in a strict sense a marker may only bear the epithet predictive after having shown that its presence or level is being followed by what was assumed by the prediction, i.e. a significantly different outcome in a prospective setting. In that sense EGFR mutations, although being correlated with prognosis too, seem to be quite accurate in predicting a response to gefitinib and erlotinib. In a phase II study from Japan, objective (complete + partial) response to gefitinib was predicted in 75% by EGFR mutation, and mutation- positive Spanish patients had an objective response to erlotinib in 82% while a 85% response rate was seen in a single-institution mutation-positive series from The Netherlands [18.Inouie A. Suzuki T. Fukuhara et al.Prospective phase II study of gefitinib for chemotherapy naïve patients with advanced non-small-cell lung cancer with epidermal growth factor receptor gene mutations.J Clin Oncol. 2006; 24: 3340-3345Crossref PubMed Scopus (475) Google Scholar, 19.Paz-Ares L. Sanchez J.M. García-Velasco A. et al.A prospective phase II trial of erlotinib in advanced non-small cell lung cancer (NSCLC) patients (p) with mutations in the tyrosine kinase (TK) domain of the epidermal growth factor receptor (EGFR).Proc Am Soc Clin Oncol. 2006; 24 (18S) (Abstr 7020)PubMed Google Scholar, 20.van Zandwijk N. Mathy A. Boerrigter L. et al.EGFR and KRAS mutations as criteria for treatment with tyrosine kinase inhibitors: retro-and prospective observations in non-small-cell lung cancer.Ann Oncol. 2007; 18: 99-103Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar]. Mature survival data of these series is not available yet but it seems unlikely that response duration will be far different from that observed in patients with mutations discovered retrospectively. A salient point of the last two studies is that exon 19 deletions are associated with higher response rates and longer disease-free intervals. Other prospective trials aiming to confirm the predictive value of EGFR mutations are still ongoing (Target trial, PI: T. Lynch) and it is obvious that similar prospective approaches with IHC and/or increased EGFR gene copy number are awaited with great interest. If these additional studies would reveal that increased EGFR copy numbers are responsible for the EGFR TKI-responsive cases lacking EGFR mutations or mainly target a NSCLC population with prolonged stabilization of disease when receiving EGFR TKIs, a significant step forward is being made and new tools for making individualized therapy choices are within reach.