MRI predictive factors for long-term outcomes of low rectal tumours.

Background: Low rectal cancers have poor outcomes. It has been suggested that low tumours are biologically more aggressive and tend to be more locally advanced at presentation. Pre-operative identification of prognostic factors will enable use of selective neoadjuvant therapies and possibly increase sphincter-sparing rates where oncologically safe.

Methods: A subset of 101 patients with low rectal cancer (within 5 cm of the anal verge) in a multicentre trial were studied. MRI images were reviewed by a senior radiologist, blinded to outcome. MRI-predicted tumour spread and MRI tumour regression grade (TRG) were analysed for 5-year recurrence and survival rates using a Cox regression model.

Results: On univariate analysis, advanced MRI low rectal tumour stage correlated with greater incidence of recurrence (p=0.013) and death (p=0.029) compared with earlier stage tumours. Good MRI TRG score (good response to pre-operative therapy) correlated with significantly reduced tumour recurrence rates (p=0.008) and increased survival (p=0.008) versus the poor MRI TRG score group. On multivariate analysis, good MRI TRG score was associated with reduced recurrence (p=0.003) but not survival rates.

Conclusions: This study confirms that MRI can be used to predict patients at increased risk of recurrence following surgery in low rectal cancer. This information can be used to direct pre-operative therapies and plan operative strategies. This is the first study to confirm the association between MRI TRG and long-term outcome. Poor response to neoadjuvant therapy can be used to plan use of further therapies prior to surgery to attempt to improve outcome.