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

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.

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.

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.

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.