EGFR Mutation T790M

Abstract.According to previous reports in the literature, theT790M mutation indicates an acquired resistance to tyrosine kinase inhibitors. The initial positive effect of combination chemotherapy with erlotinib as the first line of treatment correlates with several positive predictors including the type of carcinoma, non-smoking status, occurrence of rash and the presence of exon 19 EGFR gene mutation. The case of a 32-year-old, non-smoker with non-contributory history patient,who was diagnosed with adenocarcinoma in the left lung T4N0M0 stage IIIB is reported. The patient underwent 6 cycles of chemotherapy with erlotinib, gemcitabine and cisplatin,followed by complete remission. Fifteen months after commencing therapy, disease recurred over subsequent therapy with erlotinib and then gefitinib. During that time,bone and cerebral metastases with pericardial effusion were detected. The patient died 7 months later. Genetic examination of tumour tissue collected at the beginning of therapy revealed activating exon 19 mutation in the EGFR gene. Later, during the relapse,the same mutation was still present and, in addition, a T790M mutation in exon 20 of EGFR was found. The subsequently acquired resistance against both erlotinib,as well as gefitinib was most likely a result of tumor cells acquiring the T790M mutations and escaping the drug effect. The authors recommend testing for T790M mutation presence in selected patients prior to targeted therapy with tyrosine kinase inhibitors.Non-small cell lung cancer (NSCLC) represents more than 85% of all lung cancer cases. The cytostatic therapy of locally advanced NSCLC followed by pleural effusion is rarely successful. Better prognosis, especially for non-smokers,arises from targeted therapy by suppression of growth factorsignals through the inhibition of the epidermal growth factor receptor (EGFR) (1, 2). The EGFR gene product, a tyrosine kinase, has an important function in the transduction of growth signals by phosphorylation of other cascade proteins.The enzymatic reaction takes place at a specific EGFR site,the ATP-binding pocket, which is coded within the range of exons 18 through 21. Blocking of the ATP pocket by low molecular agents deactivates the EGFR function and stops transduction of the growth signal. This principle is utilized by two clinically approved low-molecular tyrosine kinase inhibitors: gefitinib (IRESSA ®) and erlotinib (TARCEVA ®).Tyrosine kinase activity is tightly regulated in normal cells,but dysregulated due to mutation in some types of cancer,including lung cancer. Malignant cells become dependent on growth signals from the mutant tyrosine kinases (3,4). In mid 2004, two groups independently reported increased clinical response to gefitinib therapy in patients carrying specific gene mutations within the tyrosine kinase ATP box domain (5).The so-called "activating EGFR mutations" mostly included deletions of several bases in exon 19, followed by less frequent substitutions in exons 18, 20 and 21. A majority of these mutations were detected in women, non-smokers and in patients with pulmonary adenocarcinomas. A higher frequency was also found in an Asian population compared to Caucasians (5). Since the first reports were published,screening for EGFR mutations has become a major theme in the targeted therapy of NSCLC,with experiments conducted on various populations. Consequently another interesting effect of EGFR mutation was discovered. It was reported that a specific mutation at exon 20 (assigned as T790M substitution) bears a negative prognostic value for targeted gefitinib therapy (6). Unlike in the case of the infamous exon 18 EGFR activating mutation, patients with the T790M substitution exhibited resistance to the tyrosine kinase agent.In this report,we demonstrate an interesting case of an erlotinib responder bearing an activating EGFR exon 19mutation who subsequently developed resistance due to a later appearance of the T790M mutation in the lung adenocarcinoma tissue.1879Correspondence to: Marek Minarik, Ph.D., Laboratory for Molecular Genetics and Oncology, Genomac International, Bavorska 856, CZ-15541, Prague, Czech Republic. Tel: +420 224458048, Fax: +420224458021, e-mail: mminarik@Key Words: NSCLC, EGFR mutation, T790M, erlotinib, gefitinib.A NTICANCER R ESEARCH 27: 1879-1882(2007)Acquired Resistance of Pulmonary Adenocarcinoma to Initially Successful Targeted Therapy due to EGFR Mutation T790MD. JANCARIKOVA 1, M. PESEK 1, L.BENESOVA 3, O. TOPOLCAN 2, L. HOLUBEC Jr.2and M. MINARIK 31Department of Tuberculosis and Respiratory Diseases, 2Second Department of Internal Medicine, Charles University, Medical School and Teaching Hospital Plzen;3Laboratory for Molecular Genetics and Oncology, Genomac International,Prague, Czech Republic0250-7005/2007 $2.00+.40A NTICANCER R ESEARCH 27: 1879-1882(2007)Figure1.Chest X-ray after the admission to the Pulmonary Department.Case Report1880the patient was still being treated with erlotinib. Subsequent application of an alternative tyrosine kinase inhibitor (gefitinib) and another oncology therapy did not influence further progression.The initial reports on the importance of certain EGFR mutations for a positive response to targeted biological therapy were published after the patient’s death; therefore,all genetic testing was performed post-mortem on archived tissue material. The EGFR testing was directed at mutations in exons 18-21 covering the complete tyrosine-kinase domain (Figure 4). A single EGFR mutation, a deletion of several bases in exon 19,was detected in a sample taken from the tumor prior to erlotinib therapy. This type of mutation is generally assumed to be a predictor for positive response to tyrosine kinase inhibitory agents. In addition, the retrospective analysis performed on the TALENT study data confirmed synergy between chemotherapy and targeted therapy in patients with activating EGFR mutations or non-smoking status (6). Our patient exhibited both of these predictors, hence, the remission was achieved in fullJancarikova et al : Resistance of Pulmonary Adenocarcinoma due to EGFR Mutation T790M1881Figure4.The position of T790M mutation in exon 20 of EGFR gene.Figure 2.CT examination 15 months from the beginning of the therapy.Figure 3.Chest X-ray 21 months from the beginning of the therapy.agreement with the general expectations. The appearance of a rash further indicated positive response to erlotinib during the combination treatment (7).Tests performed on a sample obtained at the time of disease progression confirmed the exon 19 deletion. In addition, however, presence of a second EGFR mutation, the T790M substitution in exon 20, was discovered. The T790M is believed to be responsible for resistance to gefitinib therapy. Whether the subsequent mutation was acquired de novo during the initially successful erlotinib therapy, or whether a small undetectable population of T790M cells was present within the tumor tissue initially is unknown. Such a resistant clone could then selectively proliferate and become the major tumor cell population as the T790M-negative cells are eradicated by the therapy. Considering the general low frequency of the T790M mutation found in NSCLC patients prior to treatment, the de novo model appears more likely in the presented case. The fact that the T790M cells also exhibited the original exon 19 mutation seems to indicate a common origin of all tumor cells,with a subpopulation acquiring the T790M resistant mutation.It is clear that in order to further demonstrate the involvement of T790M, further patients would have to be screened prior, during and after the therapy. Experiments conducted on limited number of patients and cell lines published by other groups indicate that a rise of T790M,as well as other EGFR mutations,is linked to the therapy itself, rather than clonal selection from the originally affected cell population. If confirmed, the detection of specific mutations may become useful for rational therapy selection as well as for monitoring of resistance during the therapy. This would include, in particular, patients with additional predictors, such as non-smokers with adenocarcinomas, with good quality of life and with disseminated lung adenocarcinomas and bronchioloalveolar carcinomas.AcknowledgementsThis work was supported by Internal Grant Agency of the Czech Ministry of Health, project no. NR/9087-3.References1 Novotny J, Vitek P and Petruzelka L:Non-small cell lungcarcinoma. In: Clinical and Radiation Oncology for Clinical Practice. TRITON, pp. 118-128, 2005.2 Chang AE and Gharib MI: Lung cancer. In: Oncology. AnEvidence-based Approach. Springer, NY,USA, pp. 545-622, 2006.3 Bell DW, Gore I, Okimoto RA, Heymann NG and Sordella R:Inherited susceptibility to lung cancer may be associated with the T790M drug resistance mutation in EGFR. Nature Genetics 12: 1315-1316, 2005.4 Chang AE and Gharib MI: Principles of targeted and biologicaltherapies. In: Oncology. An Evidence-based Approach.Springer,NA,USA, pp. 73-91,2006.5 Pao W, Miller VA, Politi KA, Riely GJ et al:AcquiredResistance of Lung Adenocarcinomas to Gefitinib or Erlotinib Is Associated with a Second Mutation in the EGFR Kinase Domain, PLoS Medicine, March, pp.225-237,2005.6 Rosell et al:Pharmacogenomics Comes of Age in SelectingPatients for Lung Cancer Treatment, ASCO 2006 Educational book, June 2-6, Atlanta, pp.425-430, 2006.7 Clark J, Cools J and Gilliland DG:EGFR Ihibition in Non-small Cell Lung Cancer: Resistance, Once Again, Rears Its Ugly Head, Plos Medicine, March, pp.195-197,2006.Received January 31, 2007Revised March 29, 2007Accepted April 2, 2007A NTICANCER R ESEARCH 27: 1879-1882(2007) 1882。