Abstract
Abstract only
546
Background: Front-line chemotherapy for metastatic colorectal cancer (mCRC) consists of a fluoropyrimidine backbone plus either oxaliplatin (FOLFOX or XELOX) or irinotecan (FOLFIRI or XELIRI). Large, prospective trials enrolling chemotherapy-naïve patients (pts) show FOLFOX and FOLFIRI treatment to be equivalent with similar response rates. Methods: Irinotecan inhibits TOPO1, which is now a candidate marker for irinotecan treatment benefit. Thus, we retrospectively analyzed TOPO1 expression level in 49 pts with mCRC who were treated with irinotecan-containing regimens at the Lombardi Comprehensive Cancer Center between 2009 and 2014. Patient characteristics and outcomes were compiled through chart review and the effect of TOPO1 expression on clinical outcomes was assessed. TOPO1 expression in tumor tissue from each pt was analyzed using a commercially available molecular profiling (MP) service (Caris Life Sciences). Results: The median overall survival (OS) for all pts was 33.9 months (mo), defined as the time from metastasis to death or censorship. When grouped by “high” or “low” TOPO1 expression, as defined by Caris
at the time of the testing, 29 pts were high-expressers and 20 were low-expressers. High TOPO1 expressers receiving irinotecan (n = 22) had a median OS of 27.2 mo, compared with median 41.5 mo for low-expressers (n = 14) (p = 0.27). Irinotecan is conventionally given as second-line therapy. The median OS of pts receiving second-line irinotecan was 38.2 mo for high-expressers [n = 11] vs. 68.5 mo for low-expressers [n = 5]) (p = 0.32). Conclusions: Our limited data do not support the use of TOPO1 expression levels as a predictive marker for irinotecan therapy in mCRC. However, our conclusions are limited by small sample size, lack of a control group to distinguish prognostic from predictive markers, and timing of TOPO1 measurement, which in many cases was after irinotecan therapy. Physicians currently lack an evidence-based way to choose between potentially efficacious regimens for mCRC. More rigorous studies are needed to assess the benefit of MP in mCRC care. We are currently planning a prospective study with the hope of validating the use of TOPO1 expression as a predictive marker for treatment of this disease.