Molecular follow-up of first-line treatment by osimertinib in lung cancer: Importance of using appropriate tools for detecting EGFR resistance mutation C797S.

The C797S mutation encoded by EGFR exon 20 is classically observed as a tertiary event in EGFR-mutant non-small-cell lung carcinoma (NSCLC) primarily treated by first generation tyrosine kinase inhibitors (TKI) and secondarily treated by third-generation TKI, such as osimertinib, if the EGFR-T790M resistance mutation is detected. Recently, significant prolonged progression free survival has been observed following first-line osimertinib, in EGFR-mutant NSLC. While mechanisms of molecular resistance to first-generation TKI have been well studied, little is known about resistance induced by primary third-generation TKI treatments. We report the case of a 65 year-old female treated by first-line osimertinib for a multimetastatic exon 19-EGFR-mutant NSCLC. EGFR-C797S resistance mutation and PIK3CA mutation were detected together with the remaining EGFR-exon 19 deletion. This observation provides insights of acquired resistance to first line-osimertinib. It also highlights the importance of making molecular platforms which perform routine EGFR testing in lung cancer aware of the kind of therapeutic protocols given to the patient. Indeed, for rapid results or low-costs procedures, some targeted methods specifically targeting T790M may be used at relapse and may overlook alterations such as C797S or PIK3CA mutations. Targeted next generation sequencing is therefore a recommended option.

MET immunolabelling is a useful predictive tool for MET gene amplification in glioblastoma.

AIMS: MET gene amplification is rare in glioblastoma (GBM) and represents a potential target for MET inhibitors. An immunohistochemical screening may be useful to identify MET amplification. The aim of our study was to establish how MET immunolabelling correlates with MET amplification. METHODS: Three cohorts including 108 GBM (cohort 1, prospective), 104 GBM (cohort 2, retrospective) and 52 GBM (cohort 3, prospective) were investigated for MET expression by immunohistochemistry. MET amplification was assessed by comparative genomic hybridization on microarray (CGH-array) in all cohorts and by fluorescent in situ hybridization (FISH) in cohorts 2 and 3. Active form of MET was assessed using p-MET (Y1349) immunohistochemistry. RESULTS: Diffuse MET amplification detectable by CGH-array was associated with diffuse, strong MET immunolabelling (four cases in cohort 1 and one case in cohort 2). Focal MET amplification detectable only by FISH was observed in small foci of strongly immunopositive cells in two GBM (cohort 2). In both cohorts, MET amplification was never detected in GBM devoid of strongly immunopositive cells. MET overexpression, observed in 23% of unamplified GBM, was associated with a predominant weak-to-moderate staining intensity and with necrosis (P < 0.005). p-MET was detected in all MET-amplified GBM and in perinecrotic areas of nonamplified GBM. A strong MET immunostaining intensity, at least focal and distant from necrosis, showed 100% sensitivity and 84% specificity for predicting MET amplification in cohort 3. CONCLUSIONS: MET amplification is characterized by strongly immunopositive cells. Only GBM showing strong MET immunostaining is appropriate for the assessment of MET amplification.