Standardized uptake value on ¹⁸F-FDG-PET/CT is a predictor of EGFR T790M mutation status in patients with acquired resistance to EGFR-TKIs

Background The development of epidermal growth factor receptor (EGFR) T790M point mutation in exon 20 (T790M) is the most common mechanism of resistance to EGFR tyrosine kinase inhibitors (EGFR-TKIs). The purpose of this study was to determine the association of ¹⁸F-2-fluoro-2-deoxyglucose-positron emission tomography/computed tomography (FDG–PET/CT) metrics with T790M status after acquiring resitance to EGFR-TKI resistance. Methods We retrospectively reviewed 34 advanced non-small cell lung cancer (NSCLC) patients harboring EGFR mutation who underwent rebiopsy and FDG–PET/CT before rebiopsy. These patients were evaluated for baseline characteristics, initial response to EGFR–TKIs, site of rebiopsy, overall survival, and FDG–PET/CT metrics, such as standardized uptake value (SUV), metabolic tumor volume, and total lesion glycolysis of the rebiopsy site. Results The median age was 67 years (range, 37–86 years); 19 of the patients (56%) were men. Histologic examination revealed adenocarcinoma in all but one patient, with 20 patients (59%) having stage IIIB and IV disease. Upon initial mutational analyses, the types of EGFR mutation included 17 (50%) deletions in exon 19 and 17 (50%) L858R point mutations in exon 21. At the time of acquired resistance to EGFR-TKIs, T790M mutation was identified in 20 (59%) patients. T790M-positive patients had significantly lower levels of median SUV_mean and median SUV_max of the rebiopsy site on FDG–PET/CT, compared with T790M-negative patients (SUV_mean: 4.57 vs. 9.91, P = 0.0069; SUV_max: 7.26 vs. 16.06, P = 0.0054). The survival in patients who acquired T790M after failure of EGFR-TKIs was significantly longer than those without T790M (10.2 mos. vs. 18.6 mos., P < 0.05). Conclusion T790M status was associated with lower levels of SUV_mean and SUV_max on FDG–PET/CT and significantly longer survival.