Fatty acid synthase overexpression in colorectal cancer is associated with microsatellite instability, independent of CpG island methylator phenotype.

Overexpression of fatty acid synthase (FASN), a key enzyme for de novo lipogenesis, is observed in many cancers including colorectal cancer and is associated with poor clinical outcomes. Cellular FASN expression is physiologically upregulated in a state of energy excess. Obesity and excess energy balance have been known to be risk factors for colorectal cancer. High degree of microsatellite instability (MSI-H) is a distinct phenotype in colorectal cancer, associated with CpG island methylator phenotype (CIMP). Previous data suggest that obesity or altered energy balance may potentially modify risks for MSI-H cancers and microsatellite stable (MSS) cancers differently. However, the relationship between MSI and FASN overexpression has not been investigated. Using 976 cases of population-based colorectal cancer samples from 2 large prospective cohort studies, we correlated FASN expression (by immunohistochemistry) with MSI, KRAS and BRAF mutations, p53 expression (by immunohistochemistry), and CIMP status [determined by MethyLight for 8 CIMP-specific gene promoters including CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3, and SOCS1]. Marked (2+) FASN overexpression was observed in 110 (11%) of the 976 tumors and was significantly more common in MSI-H tumors (21% [28/135]) than MSI-low (5.6% [4/72], P = .004) and MSS tumors (11% [72/678], P = .001). The association between FASN overexpression and MSI-H persisted even after stratification by CIMP status. In contrast, FASN overexpression was not correlated with CIMP after stratification by MSI status. Fatty acid synthase overexpression was not significantly correlated with sex, tumor location, p53, or KRAS/BRAF status. In conclusion, FASN overexpression in colorectal cancer is associated with MSI-H, independent of CIMP status.