Expression of folate pathway regulators and pemetrexed (pem) activity in patients (pts) with advanced non-small cell lung cancer (NSCLC).

Abstract

7585 Background: Thymidylate synthase (TS) expression has been reported to predict pem activity in pts with advanced NSCLC. Besides TS, pem inhibits multiple enzymes of the folate pathway including dihydrofolate reductase (DHFR), glycinamide ribonucleotide formyltransferase (GART) and aminoimidazole carboxamide ribonucleotide formyltransferase (AICAR). Aim of present study was to investigate whether these or other biomarkers influence pem activity in NSCLC pts. Methods: Advanced pretreated NSCLC pts who received at least two cycles of single agent pem were considered eligible if they had available tumor tissue to assess at least one of the proposed biomarkers. TS, DHFR, GART and AICAR protein expression was assessed by immunohistochemistry (IHC) in FFPE tumor samples. Pts were grouped as IHC+ and IHC– according to staining intensity. Additionally, presence of EGFR and KRAS mutations was investigated. Results: Ninety-six pts were included in the study. The majority of subjects was male (72%), smokers (93%), with adenocarcinoma (72%). Response rate (RR), disease control rate (DCR), progression-free survival (PFS) and overall survival (OS) were 12%, 47%, 2.3 and 9.5 months, respectively. Most pts resulted TS-(72%), AICAR-(82%), DHFR+ (68%), GART- (61%). EGFR and KRAS mutations were identified in 15% and 25% of assessable cases. None of the biomarkers was significantly associated with pts characteristics (gender, histology, smoking status), nor with RR or DCR. GART- pts experienced longer PFS when compared with the GART+ group (HR 0.56, p=.052), while no difference was observed according to TS, DHFR and AICAR status. A significantly longer OS was observed for TS- (HR 0.52, p=.012), GART- (HR 0.50, p=.037) and AICAR- (HR 0.40, p=.028) pts. No significant difference in the distribution of EGFR mutant pts receiving EGFR TKIs after pem failure was observed between IHC+ and IHC- groups. Conclusions: Low TS, GART and AICAR protein expression predicts significantly prolonged survival in single agent pem-treated pts with advanced NSCLC. The lack of PFS difference according to TS and AICAR status suggests prognostic rather than predictive relevance for these biomarkers.