MRI-staging after neoadjuvant therapy

The Pelican Cancer Foundation estimates that more than 14,500 new patients are diagnosed with cancer of the rectum every year in the UK. This accounts for 27% of all newly diagnosed bowel cancers. Traditionally, post-operative treatment, such as chemoradiotherapy, was given to patients following excision of advanced tumours. Despite this post-operative treatment and advances in surgical techniques, tumour recurrence rates in this group of patients remained high. The original MERCURY initiative (Magnetic Resonance Imaging in Rectal Cancer European Equivalence Study) was set up in 2001 as a prospective, European, multidisciplinary project with the aim of demonstrating the advantages of the use of MRI as a method for assessing rectal cancer, allowing features of the tumour to be identified preoperatively and allowing optimal treatment for each patient to be planned by a multidisciplinary team (MDT) prior to surgery. The results of MERCURY were published in the BMJ in September 2006.1 and has also been cited in the research evidence for ‘Improving Outcomes in Colorectal Cancer’ from The National Institute of Health and Clinical Excellence. The MERCURY study group consists of a collaboration of specialist colorectal multidisciplinary teams from 12 hospitals in the UK, Sweden, Germany and Norway. Each team consists of surgeons, radiologists, oncologists, pathologists and nurses. The chief investigator for the group is Dr Gina Brown, a consultant radiologist and imaging research lead at the Royal Marsden Hospital in London. Explaining more about the history of the project, Dr Brown said: “Traditionally, it was not general practice for rectal cancer patients to be staged using information from MRI scans. Even if patients were staged this way the information that was obtained from the scan was not necessarily of the same standard and detail across the country. The MERCURY project was set up to look at this issue. “We created a reporting proforma which required all the radiologists participating in the study to record a great deal of information relating to the stage and depth of the tumour – information that traditionally may not have been routinely recorded. The initial findings showed that, when comparing the imaging with the pathology there was extremely good agreement with the final pathology. The original MERCURY study provided us with enough evidence to say that all patients should be staged using MRI scans and that the information from this will enable a multidisciplinary team to make some preliminary decisions about whether the patient should go straight to surgery or whether they should be offered pre-operative treatment.

The MERCURY experience

Following on from the original MERCURY project, the results of the follow-up MERCURY Experience study have now been published in the Journal of Clinical Oncology.2 This study went on to look at the relevance of post-neoadjuvant therapy MRI assessment in predicting survival outcomes before undertaking any surgical procedure. The study group has been able to develop an MRI-based tumour regression grading (TRG) system (based on histopathological grading) to show how well a tumour has responded to neoadjuvant treatment. Dr Brown explained: “We created a five-point scale that demonstrates, on a rising scale, how well the tumour has responded. A score of 4 or 5, for example, would mean that hardly any fibrosis of the tumour has occurred. If MRI shows that nearly all of the tumour has been reduced to a scar at the end of neoadjuvant treatment, we know that the patient has responded well to treatment and should have a good outcome following surgery. The scarring left by dead tumour looks very different on an MRI scan to that of a living tumour, allowing for the quantification of how well the tumour has responded to treatment. We could also hypothesise that patients showing little sign of scar formation would not have such a good outcome if they were sent straight to surgery. “We have identified a big difference between disease free survival and overall survival for patients, using the MRI-based tumour regression grade system. If you are able to stage the effects of any neoadjuvant therapy before moving on to surgery it provides the opportunity for the MDT to consider further pre-treatments or to reconsider the chosen surgical procedure undertaken, allowing the team to ensure that all steps are taken to ensure the best possible outcome for the patient. “Rather than assuming that the chosen pre-treatment has worked and proceeding with the surgery, it is better to first assess the treatment response, which might lead to a decision being made not to operate, if all that is left of the cancer is a scar. This would be particularly useful for elderly or frail patients. “There is not a one-size-fits all approach for every cancer patient. It is necessary to undertake an initial assessment to see how resectable the cancer might be. For those that are easily resectable we would not want to give any radiotherapy treatment because it would mean the patient had to suffer from unwanted and unnecessary side effects. There might also be a functional issue post-therapy, which would be another important consideration for the patient. We want to save patients from having unnecessary over-treatment. Conversely, the surgeon may underestimate the scale of the disease, so it is useful for the cancer to be assessed initially and for the patient to get the optimum treatment before surgery.” Dr Brown went on to explain the next steps for the MERCURY study group: “The next stage of our research will look at the long-term patient outcome in cases where, following successful neoadjuvant therapy, it is decided that surgery is not necessary.