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Fumarate hydratase expression in localized, radically-resected clear cell renal cell carcinoma and its association with clinical outcomes.

620 Background: Prognostic stratification of localized clear cell renal cell carcinoma (lccRCC) mainly relies on clinical characteristics and TNM staging system, while biological biomarkers are currently lacking. We previously showed that reduced expression of the tricarboxylic acid cycle enzyme fumarate hydratase (FH) was associated with better clinical outcomes in patients (pts) with metastatic ccRCC. In the present study we aimed at assessing the association between intratumor FH expression and clinical outcomes in pts with radically-resected lccRCC. Methods: Pts with radically-resected lccRCC and available formalin-fixed, paraffin-embedded (FFPE) primary (renal) tumor tissue were included. FH protein expression was assessed by means of immunohistochemistry (IHC) and defined as normal (comparably to non-neoplastic tubular cells) or low (lower than in non-neoplastic tubular cells). Results: Out of 50 pts included, we found a normal FH expression in 20 cases (40%) and a low FH expression in 30 cases (60%). Median age was 57 years (interquartile range 49-68) and 48 pts (96%) had pN0 disease, while 2 pts (4%) had pN1 disease. Low FH expression was associated with pT ( P= .003) but not with sex, age, Fuhrman grade or pN. After a median follow-up of 76.9 months, low FH expression was associated with a lower relapse rate (13% vs 50%; odds ratio for relapse 0.16; 95% confidence interval [CI] 0.04-0.62; P= .005), longer relapse-free survival (RFS) (5-years RFS rate 90% vs 50%; HR 0.20; 95% CI 0.06-0.63; P= .006) and a trend toward a better overall survival (OS) (5-years OS rate 100% vs 77.3%; HR 0.14; 95% CI 0.02-1.23; P= .07) when compared with normal FH expression. In the multivariable model including other characteristics associated with RFS, low FH expression confirmed an independent association with RFS (adjusted HR 0.25; 95% CI 0.06-0.91; P= .03). Conclusions: In our study, low intratumor FH, as detected by IHC, was associated with lower relapse rate, better RFS and a trend toward a better OS in patients with lccRCC when compared with normal FH levels. The role of FH expression as a prognostic biomarker in this setting warrants further investigation.