• Eric Santoni-Rugiu, Morten Grauslund, Linea C Melchior, Junia C Costa, Jens B Sørensen, and Edyta M Urbanska.
• Department of Pathology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark. Electronic address: eric.santoni-rugiu.02@regionh.dk.
• Lung Cancer. 2017 Nov 1; 113: 14-17.

AbstractPatients with epidermal growth factor receptor (EGFR) gene-mutated non-small cell lung cancer (NSCLC) obtain substantial clinical benefit from EGFR tyrosine-kinase inhibitors (TKIs), but will ultimately develop TKI-resistance resulting in median progression-free survival of 9-15 months during first-line TKI-therapy. However, type and timing of TKI-resistance cannot be predicted and several mechanisms may simultaneously/subsequently occur during TKI-treatment. In this respect, we present a 49 year-old Caucasian male ex-smoker with metastatic pulmonary adenocarcinoma (ADC) that concomitantly harbored an EGFR exon 19-mutation (p.E746_A750delELREA) and a previously unreported 2bp frame-shift microdeletion in the fibroblast growth factor receptor 3 (FGFR3; p.D785fs*31) gene. Interestingly, FGFR3-mutations have previously been described in other cancer types of Caucasian patients and may represent an alternative pathway to EGFR-signaling. The patient received first-line erlotinib but after only 7 weeks showed metastatic pleural effusion, in which transformation to small cell lung cancer (SCLC) that retained the EGFR- and FGFR3-mutations was identified. Consequently, standard carboplatin-etoposide regimen for SCLC combined with erlotinib continuation was implemented obtaining significant objective response. However, after completing 6 cycles of this combination, new pulmonary and hepatic metastases appeared and showed persistence of the original EGFR- and FGFR3-mutated ADC phenotype together with acquisition of the erlotinib-resistant T790M EGFR-mutation. The patient rapidly deteriorated and deceased. Thus, this advanced EGFR-mutated NSCLC displayed very rapid onset and heterogeneous genetic and phenotypic mechanisms of TKI-resistance occurring at different times and locations of metastatic disease: concomitant FGFR3-mutation before and during TKI-treatment as potential intrinsic mechanism for the rapid progression; transformation to SCLC at first progression during TKI-therapy; acquired T790M EGFR-mutation at second progression. Our case also underlines that, when achievable, rebiopsies of progressive sites during TKI-treatment are important for identifying heterogeneous histopathological and molecular resistance mechanisms and better defining possible treatment modifications.Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

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