Rectal cancer is less common than cancer of the colon; however, it is anticipated that nearly 40,000 individuals in the US will be diagnosed with rectal cancer in 2011 (Siegel, Ward, Brawley & Jemal, 2011). The current standard of care for rectal cancer is extended-course radiotherapy or neoadjuvant combination chemoradiotherapy together with total mesorectal excision (TME) surgery (NCCN, 2011). Certain imaging techniques, including magnetic resonance imaging (MRI), enable appropriate selection of patients on the basis of assessment of locally advanced disease and the relationship of tumor to the potential resection margin. High resolution MRI has been used to assess tumor response before surgical resection, but the relevance of post-treatment MRI assessment in predicting survival outcomes has not been investigated (Patel et al, 2011).
The Patel et al study (2011) is a subgroup analysis of a 2002 prospective study (MERCURY Study Group, 2006) that evaluated the diagnostic accuracy of MRI staging in a consecutive series of patients with biopsy-proven rectal cancer undergoing TME surgery with histopathology as the reference standard.
Study Details (Patel et al, 2011):
To assess magnetic resonance imaging (MRI) and pathologic staging after neoadjuvant therapy for rectal cancer in a prospectively enrolled, multicenter study.
In a prospective cohort study, 111 patients who had rectal cancer treated by neoadjuvant therapy were assessed for response by MRI and pathology staging by T, N and circumferential resection margin (CRM) status. Tumor regression grade (TRG) was also assessed by MRI. Overall survival (OS) was estimated by using the Kaplan-Meier product-limit method, and Cox proportional hazards models were used to determine associations between staging of good and poor responders on MRI or pathology and survival outcomes after controlling for patient characteristics.
On multivariate analysis, the MRI-assessed TRG (mrTRG) hazard ratios (HRs) were independently significant for survival (HR, 4.40; 95% CI, 1.65 to 11.7) and disease-free survival (DFS; HR, 3.28; 95% CI, 1.22 to 8.80). Five-year survival for poor mrTRG was 27% versus 72% (P = .001), and DFS for poor mrTRG was 31% versus 64% (P = .007). Preoperative MRI-predicted CRM independently predicted local recurrence (LR; HR, 4.25; 95% CI, 1.45 to 12.51). Five-year survival for poor post-treatment pathologic T stage (ypT) was 39% versus 76% (P = .001); DFS for the same was 38% versus 84% (P =.001); and LR for the same was 27% versus 6% (P =.018). The 5-year survival for involved pCRM was 30% versus 59% (P = .001); DFS, 28 versus 62% (P = .02); and LR, 56% versus 10% (P = .001). Pathology node status did not predict outcomes.
The investigators in the Patel et al subgroup analysis study (2011) concluded that MRI assessment of TRG and CRM are imaging markers that predict survival outcomes for good and poor responders and provide an opportunity for the multidisciplinary team to offer additional treatment options before planning definitive surgery. Postoperative histopathology assessment of ypT and CRM but not post-treatment N status was important postsurgical predictors of outcome.
This is the first prospective study that has demonstrated a correlation between radiologically-determined tumor response and long-term outcomes. Although rectal cancer affects far fewer people than colon or some of the other more common cancers, advances in the use of imaging techniques to predict survival outcomes prior to definitive surgery can translate to better patient quality of life, improved overall survival and better use of costly healthcare resources. Oncology professionals have relied on the degree of nodal involvement in predicting pelvic recurrence. In the current era of TME as standard of care, pre-surgical MRI assessment may well be a better predictor of local recurrence than post-surgical pathohistological assessment.
National Comprehensive Cancer Network (NCCN). (2011). Clinical Practice Guidelines in Oncology. Rectal Cancer v.1.2012. Retrieved from http://www.nccn.org/professionals/physician_gls/pdf/rectal.pdf Free access after registration.
Patel, U.B., Taylor, F., Blomqvist, L., George, C., Evans, H. Tekkis, P.,…Brown, G. (2011). Magnetic Resonance Imaging–Detected Tumor Response for Locally Advanced Rectal Cancer Predicts Survival Outcomes: MERCURY Experience. Journal of Clinical Oncology, 29, epub ahead of print August 29, 2011. doi: 10.1200/JCO.2011.34.9068 Link to abstract http://www.ncbi.nlm.nih.gov/pubmed/21876084
Siegel, R., Ward, E., Brawley, O., & Jemal, A. (2011). Cancer statistics, 2011: The impact of eliminating socioeconomic and racial disparities on premature cancer deaths. CA: Cancer Journal for Clinicians, 61, 212-236. doi:10.3322/caac.20121 Link to free full text http://onlinelibrary.wiley.com/doi/10.3322/caac.20121/pdf
MERCURY Study Group. (2006). Diagnostic accuracy of preoperative magnetic resonance imaging in predicting curative resection of rectal cancer: Prospective observational study. BMJ, 333, [epub on September 19, 2006] doi:10.1136/bmj.38937.646400.55 Link to free full text http://www.bmj.com/content/333/7572/779.full.pdf