Use of MRI-defined tumor distance from the anal verge to predict tumor response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer.

Abstract

573 Background: Neoadjuvant Chemoradiotherapy (CRT) and surgical resection is the current standard management for patients with locally advanced rectal cancer (i.e. T3 or 4 N0/1 M0) (LARC). Tumour predictive factors for response to CRT in rectal cancer remain controversial. Staging investigations are not standardised and MRI has not been used consistently to approach this. The aim of this study is to investigate whether tumour distance from anal verge, as measured on MRI, is a predictive factor for response to CRT in LARC. Methods: This is a retrospective study. Patients with LARC or low T2 N0/1 M0 rectal cancer (i.e. ≤ 5cm from anal verge measured by MRI) treated with preoperative CRT in 2003- 2009 were included. Pelvic MRIs acquired before CRT and no less than 4 weeks post CRT were reviewed. Patients with ypT0-2 in the resected specimen were classified as responders because ypT0-2 has been shown with significant OS and DFS benefit (Valentini V et al. Int J Radiat Oncol Biol Phys. 2002; 53(3): 664-74). Downstage of mrT2 low rectal cancer was defined as ypT0-1 post CRT. Univariate binary logistic regression (UBLR) was used to analyse the predictor associated between responders and non-responders to CRT treated in the same period of time. Results: 281 patients with LARC who underwent CRT were included in the study. 96% patients in this study had T3/T4 LARC and 4% had T2 low rectal cancer. 114 (41%) were responders as defined above, 167 (59%) were non-responders to CRT. The mean MRI defined tumour distance from anal verge was significantly less in responders (6.4cm [Confidence Intervals (CI) = 5.7 -7.1]) when compared with non-responders (7.9cm [CI =7.3 – 8.6]) (P<0.05). Conclusions: The UBLR analysis from our study indicated that an MRI measured tumour distance of ≤ 5cm from the anal verge independently predicted higher tumour downstaging rate (p < 0.001) to CRT in LARC. Further investigation is recommended regarding tumour downstaging and sphincter preserving surgical resection rate in low rectal cancer post neoadjuvant CRT. [Table: see text]