Why was the study needed?
About 42 000 new cases of colorectal cancer are diagnosed each year in the UK. More than 16 000 people die from the disease annually. Treatment options depend on the stage of the cancer and particularly whether metastases have been identified.
Current staging pathways are based on a sequence of imaging tests, such as computerised tomography (CT), positron emission tomography/computerised tomography (PET-CT), and magnetic resonance imaging (MRI). These differ in their usefulness for detecting metastases in different body parts. Whole body MRI could be an alternative initial investigation to the current complex pathways, but evidence is lacking on how effective it could be for colorectal cancer staging.
This study aimed to compare the diagnostic accuracy of whole body MRI staging pathways with standard pathways. It also investigated any differences in staging times, extra tests, costs, and treatment decisions.
What did the study do?
This diagnostic accuracy study included 299 adults with a new diagnosis of colorectal cancer from 16 hospitals in the UK. Participants had whole body MRI, as well as the other standard staging investigations.
Initial treatment decisions were made using only the usual care investigations. Then the MRI findings were revealed. The clinicians decided which additional tests they would want in order to make a decision, and these were arranged if they had not already been done. Finally, treatment decisions were made based on all the investigations together.
The opinion of an expert multidisciplinary review panel, based on all initial investigations and follow-up data at 12 months, were used as the reference to act as the “correct” or true diagnosis for the comparison.
What did it find?
• The pathways were similar in their ability to identify metastatic disease correctly (sensitivity) in those later proved to have them; this was 67% for whole body MRI compared with 63% for standard pathways (difference 4%, 95% confidence interval -5% to 13%).
• There was no difference between the pathways in their ability to diagnose correctly the stage of those without metastases (specificity), which was 95% for whole body MRI versus 93% for standard pathways (difference 2%, 95% confidence interval -2% to 6%).
• Decisions made using either pathway were the same as the decisions made by the review panel 96% of the time for whole body MRI and 95% for the standard pathway.
• The median length of the staging process was shorter for whole body MRI, 8 days (95% confidence interval 6 to 9) compared with 13 days for standard pathways (95% confidence interval 11 to 15). Whole body MRI pathways required just one test on average, including whole body MRI, compared with two tests for standard pathways.
• Average costs per patient were lower for the whole body MRI group at £216 (95% confidence interval £211 to £221), compared with £285 for the standard pathway group (95% confidence interval £260 to £310).
What does current guidance say on this issue?
The National Institute for Health and Care Excellence updated its guideline on the diagnosis and management of colorectal cancer in 2014. It does not recommend MRI for initial diagnostic investigations. It recommends contrast enhanced CT of the chest, abdomen, and pelvis to estimate the stage of disease for all patients diagnosed with colorectal cancer.
For patients with colon cancer, the guideline recommends no further routine imaging is needed. For patients with rectal cancer, it recommends MRI to assess the risk of local recurrence.
This guidance is currently being reviewed, with an update expected to be published in January 2020.
What are the implications?
This study suggests that whole body MRI is accurate enough to replace other tests for diagnosis, staging, and planning treatment of colorectal cancer. The whole body MRI pathway gave similar results to current pathways in terms of identifying metastatic disease and resulted in the same treatment decisions. It also reduced the number of tests needed, sped up the staging process, and lowered the costs.
The study reflects how imaging is currently carried out and interpreted in UK hospitals, although half of them were not currently able to offer whole body MRI themselves, and this had to be done by a nearby hospital.
The findings support a change in practice and may inform future updates to relevant guidance.
- Contributor: Fran Wilkie
- All authors contributed to development and review of this summary, as part of the wider NIHR Signals editorial team. RC is guarantor.
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- Competing interests The BMJ has judged that there are no disqualifying financial ties to commercial companies. The authors declare the following other interests: none
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- Cancer Research UK. Bowel cancer statistics. London: Cancer Research UK. https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/bowel-cancer
- NHS website. Bowel cancer. London: Department of Health; 2016. https://www.nhs.uk/conditions/bowel-cancer/causes/
- National Institute for Health and Care Excellence. Colorectal cancer: diagnosis and management. CG131. London: National Institute for Health and Care Excellence; 2014. https://www.nice.org.uk/guidance/cg131https://www.nice.org.uk/guidance/cg131
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