MRI-Based Treatment Decision Making for Rectal Cancer

There are a number of clinicopathologic variables that predict outcome in rectal cancer. In the era of postoperative chemoradiation treatment, these were more easily identified and were used to help select patients for adjuvant therapy. They included, but were not limited to, variables such as location of the tumor in reference to the peritoneal reflection, T stage, nodal status, resection margins, lymphatic invasion, mucin, and perineural invasion. With the movement to preoperative therapy in the 1990s, many of these variables were no longer easily assessed, and all patients with cT3 and/or N+ rectal cancer were offered preoperative chemoradiation.[1]

The most common preoperative imaging techniques in the 1990s were transrectal ultrasound and CT. Although transrectal ultrasound can identify clinical T stage with as high as 90% accuracy-and CT with approximately 60% accuracy-both are far less reliable for other important variables, such as nodal status, mesorectal invasion, and lymphatic invasion.[2] This led to both underuse and overuse of preoperative therapy and its associated short- and long-term toxicities. The introduction of high-resolution MRI, as well as the focused training of radiologists to help interpret the images, offered the opportunity to identify the relevant variables preoperatively, thereby allowing a more selective use of preoperative therapies.

The article by Dr. Glynne Jones and colleagues[3]builds on this paradigm change in preoperative therapy in rectal cancer and offers insight into the use of pelvic MRI in guiding treatment decisions. This well-written, thoughtful, and comprehensive review explores the rationale for and results of MRI-based decision making. The authors not only discuss the identification of those historic clinicopathologic variables that offered prognostic value in the postoperative setting but explore new variables that have been identified in patients being considered for preoperative therapy. Two examples of such new variables are clinical response and functional imaging. These, coupled with the historic clinicopathologic variables, have the potential to allow more selective use of both preoperative radiation therapy and chemoradiation.

Clinical treatment guidelines have begun to incorporate MRI findings. A number of guidelines have been published and are reviewed in the article. However, it should be emphasized that guidelines are living documents and will continue to evolve as expertise improves and data from prospective trials become available. Furthermore, the use of decision support analysis may allow incorporation of additional individual variables to further improve predictability. The website http://www.predictcancer.org is an example of the use of this sort of analysis to improve prediction.

As with any technology, MRI has limitations. The authors emphasize the steep learning curve associated with identifying the ideal MRI imaging sequences as well as the individual expertise required to interpret the images. Furthermore, the higher cost of the technology needs to be considered. In our view, multidisciplinary teams that have fully integrated diagnostic radiologists with robust quality assessment programs are the best equipped to achieve optimal outcomes.[4]

In summary, MRI offers the ability to build on our experience with proven clinicopathogic variables from the postoperative era as well as to include new ones identified during the preoperative era. In addition to its role in pretreatment staging, MRI is also being incorporated directly into therapy. Examples include MRI-guided surgery, in which images obtained during surgery can provide the surgeon with additional information. Another advance is MR-guided radiation, which combines MRI and radiation delivery in one machine. Potential advantages of such an approach would include the capability for real-time modification of the radiation field and dose during treatment delivery, based on the physical and biological response of the tumor. New developments in MRI offer the opportunity to improve our therapeutic results and challenge the paradigm of “one size fits all.”

Financial Disclosure:The authors have no significant financial interest in or other relationship with the manufacturer of any product or provider of any service mentioned in this article.

References:

1. Sauer R, Liersch T, Merkel S, et al. Preoperative versus postoperative chemoradiotherapy for locally advanced rectal cancer: results of the German CAO/ARO/AIO-94 randomized phase III trial after a median follow-up of 11 years. J Clin Oncol. 2012;30:1926-33.

2. Bipat S, Glas AF, Slors FJM, et al. Rectal cancer: local staging and assessment of lymph node involvement with endoluminal US, CT, and MR imaging-a meta-analysis. Radiology. 2004;232:773-83.

3. Glynne-Jones R, Tan DBH, Goh V. Pelvic MRI for guiding treatment decisions in rectal cancer. Oncology (Williston Park). 2014;28:667-77.

4. Augestad KM, Lindsetmo RO, Stulberg J, et al. International preoperative rectal cancer management: staging, neoadjuvant treatment, and impact of multidisciplinary teams. World J Surg. 2013;11:2689-700.