LAUSR

Simple Summary In breast cancer, the promising efficacy of farnesyltransferase inhibitors (FTIs) in preclinical studies is in contrast to only limited effects in clinical trials. Therefore, this study focussed on the clinical relevance of polymorphisms in FNTB, the gene encoding the catalytically active β-subunit of farnesyltransferase, in early breast cancer. This is the first study on breast cancer suggesting that FNTB promoter polymorphisms are independent prognostic biomarkers, particularly in patients with early triple negative breast cancer (TNBC), and possibly modulate FNTB transcriptional activity. Taken together, we describe for the first time, a link between FNTB promoter polymorphism and the prognosis of breast cancer patients. We propose that FNTB genotyping, which is easily possible from a single blood drawing, may allow independent prognostic stratification, particularly in TNBC, in order to identify patients with a high risk of recurrence and poor prognosis. Ultimately, our results encourage further prospective evaluations of the role of FNTB promoter polymorphisms in predicting response to FTIs, particularly in TNBC patients. Abstract In breast cancer, the promising efficacy of farnesyltransferase inhibitors (FTIs) in preclinical studies is in contrast to only limited effects in clinical Phase II–III trials. The objective of this study was to explore the clinical relevance of farnesyltransferase β-subunit (FNTB) single nucleotide promoter polymorphisms (FNTB-173 6G > 5G (rs3215788), -609 G > C (rs11623866) and -179 T > A (rs192403314)) in early breast cancer. FNTB genotyping was performed by pyrosequencing in 797 patients from a prospective multicentre observational PiA trial (NCT 01592825). In the total cohort, the FNTB-173 6G > 5G polymorphism was an independent predictor of RFI (HR = 0.568; 95% CI = 0.339–0.949, p = 0.031), OS (HR = 0.629; 95% CI = 0.403–0.980, p = 0.040) and BCSS (HR = 0.433; 95% CI = 0.213–0.882; p = 0.021), whereas the FNTB-609 G > C polymorphism was an independent predictor of RFI (HR = 0.453; 95% CI = 0.226–0.910, p = 0.026) and BCSS (HR = 0.227; 95% CI = 0.075–0.687, p = 0.009). Subtype analysis revealed the independent prognostic relevance of FNTB promoter polymorphisms, particularly in TNBC but not in luminal or HER2-positive intrinsic subtypes. Finally, we used electrophoretic mobility shift assays (EMSAs) to confirm in vitro that the polymorphism FNTB-173 6G > 5G resulted in the differential binding of nuclear proteins from five different breast cancer cell lines. This is the first study on breast cancer suggesting that FNTB promoter polymorphisms (i) are independent prognostic biomarkers, particularly in patients with early TNBC, and (ii) could modulate FNTB’s transcriptional activity.