Imaging biomarkers for risk stratification in colorectal and anal cancer

Abstract

Introduction: “Imaging biomarkers” (IB) are radiological measurements that predict outcomes. Although IBs have been validated for primary colorectal cancer none are available for predicting disease relapse in colorectal or anal cancer. The aim of this thesis was to develop and implement IBs for relapse in colorectal and anal cancer.

Methods: A systematic review assessed the completeness of reporting of IB publications in colorectal liver metastases. Potential IBs for anal SCC and mrTRG response assessment in rectal cancer were tested retrospectively. Finally IB implementation was tested by retrospectively and then prospectively assessing the potential role of DW-MRI as a screening tool for synchronous liver metastases in colorectal cancer.

Results: Systematic review (n=30) found no IB studies adhered to REMARK but there were areas of good practice. mrT staging and mr-derived depth of extramural spread (DEMS) both predicted for outcome in 131 anal SCC patients, but when combined DEMS >12mm was the only predictor of outcome. mrTRG response in 338 patients predicted for recurrent or metastatic disease (OR 3.6) and described patterns of disease. Retrospectively DW-MRI detected more synchronous liver metastases in high-risk rectal cancer than CT (OR 8.065, P=0.018) with poorer 3 year OS (p<0.05). This led to the multicentre SERENADE study which aimed to validate screening DW-MRI in 262 patients; interim analysis showed DW-MRI detected 5% more synchronous liver metastases than CT.

Conclusions and Future Work: REMARK should be required by journals publishing IB work. DEMS is a novel potential IB for anal SCC which could result in a change to TNM staging but first requires external validation against outcomes. Findings related to mrTRG and the timing and site of metastases should be considered when planning follow-up. Risk-adapted screening for liver metastases with DW-MRI has been validated and should be adopted in clinical practice for high-risk patients.