Patients with NSCLC may display a low ratio of p.T790M vs. activating EGFR mutations in plasma at disease progression: implications for personalised treatment

// Marzia Del Re 1, * , Paola Bordi 2, * , Iacopo Petrini 3, * , Eleonora Rofi 1 , Francesca Mazzoni 4 , Lorenzo Belluomini 5 , Enrico Vasile 3 , Giuliana Restante 1 , Francesco Di Costanzo 4 , Alfredo Falcone 3 , Antonio Frassoldati 5 , Ron H.N. van Schaik 6 , Christi M.J. Steendam 7 , Antonio Chella 8 , Marcello Tiseo 2 , Riccardo Morganti 9 and Romano Danesi 1 1 Clinical Pharmacology and Pharmacogenetics Unit, Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy 2 Medical Oncology Unit, University Hospital of Parma, Parma, Italy 3 Medical Oncology Unit, Department of Translational Research and New Technologies in Medicine and Surgery, University Hospital of Pisa, Pisa, Italy 4 Medical Oncology Unit, University Hospital Careggi, Firenze, Italy 5 Medical Oncology Unit, Civil Hospital Arcispedale S. Anna, Ferrara, Italy 6 Department of Clinical Chemistry, Erasmus University Medical Center, Rotterdam, The Netherlands 7 Department of Pulmonology, Erasmus University Medical Center, Rotterdam, and Amphia Hospital, Breda, The Netherlands 8 Lung Diseases Unit, Azienda Ospedaliero-Universitaria, Pisa, Italy 9 Section of Statistics, Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy * These authors have contributed equally to this work Correspondence to: Iacopo Petrini, email: iacopo.petrini@unipi.it Keywords: circulating tumor DNA, EGFR, personalized medicine, predictive biomarkers Received: July 12, 2017     Accepted: July 26, 2017     Published: September 15, 2017 ABSTRACT Introduction: NSCLC harboring activating mutations of EGFR is highly sensitive to first-line EGFR-tyrosine kinase inhibitors (TKIs), but drug resistance depending on the EGFR mutation p.T790M will occur in about 50-60% of patients. Detailed information on the amount of p.T790M plasmatic level associated with resistance to EGFR-TKIs and guidance to treatment with p.T790M-effective TKI depending on these levels, is lacking. Methods: This study enrolled p.T790M-positive patients (n=49) affected by EGFR-mutated NSCLC at progression to first-line EGFR-TKIs and, in selected cases (n=5), after second-line treatment with osimertinib. Cell-free circulating tumor DNA (cftDNA) was extracted from plasma and the quantitative analysis of EGFR ex19del, p.L858R and p.T790M was performed by digital droplet PCR. Results: The mean amount of mutated alleles at progression to first-line EGFR-TKIs was 108,492 copies/ml for ex19del, 97,336 copies/ml for p.L858R, but only 8,754 copies/ml for p.T790M. There was no significant correlation between progression-free survival and the ratio of p.T790M over EGFR activating mutations. The analysis of cftDNA in 5 patients treated with osimertinib revealed a marked decrease of all EGFR mutant alleles. Conclusions: The amount of p.T790M in plasma can be much lower than activating EGFR mutations. Despite this finding, osimertinib is effective in p.T790M-positive patients. These results indicate that clones driving resistance to EGFR-TKIs represent a minority among cells bearing activating EGFR-mutations. In addition, the identification of a threshold level of p.T790M is not a strict requirement for the selection of patients to be treated with osimertinib, since treatment showed a decrease in all EGFR mutated cells.