Feature article

MRI and small node metastases (Early detection) in rectal cancer

Rectal cancer occurs in the last several inches of the large intestine (i.e., the rectum) and it is most commonly classified in the broad category of colorectal cancer, which are cancers that originate in either the large colon or rectum.1 This broad category of colorectal cancer is the third most common cancer worldwide.2 However, according to the Colorectal Cancer Alliance,3 about 29 percent (nearly 40,000 cases in the U.S.) of colorectal cancer cases diagnosed annually originate in the rectum, and people over the age of 50 accounts for 90 percent of cases diagnosed.4

Although advancements in colorectal cancer treatment have put the overall death rate for colorectal diseases on a downward trend,5 the mortality rate remains high6 and the death rate among Americans under the age of 55 is also rising.7 Magnetic resonance imaging (MRI) is a significant contributing factor to the progress in lowering this death rate, especially in diagnosing early stage rectal cancer that has not spread beyond the small lymph nodes8 and into surrounding tissue or bones. Such early detection provided through MRI is a crucial factor in survival rates because unlike colon cancer, rectal cancer has a high rate of local reoccurrence because of its tendency to spread through the lymph node system.9

MRI is the gold standard in rectal cancer assessment21

Physicians are working worldwide to find the best ways to deploy MRI in diagnosing, assessing, and planning rectal cancer protocols and therapies. However, even though high-resolution MRI is now considered to be the gold standard in rectal cancer assessment,21 it is often not the preferred diagnostic modality.10 This is due to lingering concerns about detection of the penetration depth of early tumors.

However, a 2016 UK/Russian study review found that high-resolution MRI overcame "known limitations" of other imaging modalities for all rectal cacner applications, including staging and surgical planning.11 Such results show that unnecessary over-treatment to patients could be prevented and, among other benefits, help control healthcare spending.

Worldwide effort underway

A 2016 Chinese study team compared MRI, endoluminal ultrasound (EUS) and computed tomography (CT) in rectal tumor staging.12 The team found that while all three modalities yielded similar diagnostic accuracy, high-resolution 3.0T provided better performance at early detection. This yielded better treatment staging results, and the team recommended MRI as the preferred diagnostic modality. An Egyptian study13 conducted in 2015 that high-resolution MRI imaging with gadolinium contrast is also vital in staging rectal sphincter-sparing surgery. 

The American College of Radiology accepts MRI imaging proficiency in rectal cancer staging as the evidenced-based standard. On its learning site, it offers a rectal cancer competency-based MRI interpretation set-of guidelines.14 The protocol includes standardized reporting and patient-focused shared making decisions. The Radiological Society of North America publishes numerous guidelines for deploying MRI imaging in the evaluation of rectal cancer. In a 2012 publication15 on MRI imaging to evaluate primary rectal cancer, several determining factors unique to MRI were discussed. These MRI clinical points included: assessment; depth of the tumor; the relationship of the tumor to anatomic structures; vascular invasion; and nodal involvement. The analysis also discusses problems and solutions provided by MRI in rectal cancer, as well as practical guidelines for obtaining good-quality images.

MRI provides surgeons better sight before the first incision

Other recent studies are reviewing the relative performance of MRI diagnoses in improving rectal cancer staging and treatment decisions. A 2014 study16 in northern Europe found that the indiscriminate use of chemotherapy to shrink rectal tumors may be instead applied selectively with combined improvements in surgical procedures, MRI, and pathologic reporting. MRI’s role in this updated approach lies in its ability to inform surgeons about resection margins and other stage planning factors, such as poor prognostic and tumor features.

A 2017 South Korean report17 by the Korean Society of Abdominal Radiologists cited the value of MRI in managing rectal cancer in both the diagnostic and treatment staging phases. The report cited the challenge of differing overall management protocols between the U.S. and Europe; the authors sought to arrive at a Korean standard for its medical community. The study authors see emerging MRI rectal cancer protocols as helpful in promoting a proven, evidence-based common protocol to standardize care at the T-staging level, including nodal involvement, which can be used in daily clinical practice.

MRI is choice for assessing pelvic tumor migration of rectal cancer

While another 2016 Korean study found low correlation at 38.9 percent of MRI detection of rectal tumors at the protein level18, a 2016 Colombian study found high specificity with reproduction of colorectal tumors in assessing detection of node involvement.19 The study focused on the rate of re-occurrence of the disease, which is 70 percent in the first two years and 85 percent by the third year, according to the authors. Using MRI, the authors were able to assess the extent of the disease and compromise to adjacent organs with between 80 to 90 percent sensitivity and 100 percent specificity. The study concluded that in the hands of an expert radiologist, MRI is the method of choice for assessing the pelvis in patients with colorectal cancer.

One of the challenges in applying MRI management in rectal cancer is the variation in imaging quality between different vendors’ MRI technology. While a 2016 American article stated that MRI now plays a pivotal role in the staging of rectal cancer,20 the authors warned that MRI effectiveness could be compromised if the most rigorous of technical standards are not applied. The article referenced emerging diffusion-weighted imaging–MRI and dynamic contrast-enhanced–MRI protocols as examples of rising MRI techniques. Another possible concern is that while the worldwide focus on the use of MRI in managing the disease is admirable, there are only a few centers which have what the authors call extreme expertise. These factors can make reproducing studies and results challenging.

MRI can promote non-surgical management of rectal cancer

The authors recommend standardizing MRI rectal cancer management protocols and techniques, as well as promoting center and clinician expertise. By implementing such quality metrics, the authors believe that MRI management of rectal cancer will promote a philosophy that will preserve organs, quality of life and eventually encourage non-operative management of rectal cancer in the future.20

References:

  1. Rectal Cancer, Overview. The Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/rectal-cancer/symptoms-causes/syc-20352884 . Last accessed July 20, 2018.
  2. Worldwide data. World Cancer Research Fund International. https://www.wcrf.org/int/cancer-facts-figures/worldwide-data .  Last accessed July 20, 2018.
  3. Determine your risk – and practice prevention. Colorectal Cancer Alliance. https://www.ccalliance.org/colorectal-cancer-information/statistics-risk-factors . Last accessed July 20, 2018.
  4. Imaging Tests for the Staging of Colorectal Cancer. Agency for Healthcare Research and Quality. https://effectivehealthcare.ahrq.gov/topics/colorectal-cancer-staging/research-protocol .
  5. Cancer Stat Facts: Colorectal Cancer. National Cancer Institute.
  6. https://seer.cancer.gov/statfacts/html/colorect.html. Last accessed July 20, 2018.
  7. Pelvic MRI for Guiding Treatment Decisions in Rectal Cancer.  http://www.cancernetwork.com/oncology-journal/pelvic-mri-guiding-treatment-decisions-rectal-cancer . Last accessed July 20, 2018.
  8. Colorectal Cancer Mortality Rates in Adults Aged 20 to 54 Years in the United States, 1970-2014. JAMA Network.   https://jamanetwork.com/journals/jama/fullarticle/2647859 . Last accessed July 20, 2018.
  9. Lymph Nodes and Cancer. American Cancer Society.  https://www.cancer.org/cancer/cancer-basics/lymph-nodes-and-cancer.html . Last accessed July 20, 2018.
  10. Analysis of Risk Factor for Lymph Node Involvement in Early Stages of Rectal Cancer… International Journal of Surgical Oncology  https://www.hindawi.com/journals/ijso/2012/438450/. Last accessed July 20, 2018.
  11.  Sveltlana Balyasnikova & Gina Brown. Optimal Imaging Strategies For Rectal Cancer Staging and Ongoing Management. June 2016. Current Treatment Option in Treating Cancerhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC4891388/. Last accessed September 6, 2018.
  12. Evaluating rectal tumor staging with (MRI), (CT), and endoluminal ultrasound. Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5591164/ . Last accessed July 20, 2018.
  13. Role of (MRI) in the Assessment of rectal neoplasms. The Egyptian Journal of Radiology and Nuclear Medicine. https://www.sciencedirect.com/science/article/pii/S0378603X15002028 . Last accessed July 20, 2018.
  14. Rectal Cancer Staging: A Competency-Based Assessment of MR Imaging Proficiency. American College of Radiology.  https://www.acr.org/Lifelong-Learning-and-CME/Learning-Activities/Rectal-Cancer-Staging . Last accessed July 20, 2018.
  15. MR Imaging for Preoperative Evaluation of Primary Rectal Cancer: Practical Considerations. RadioGraphics.https://pubs.rsna.org/doi/full/10.1148/rg.322115122 . Last accessed July 20, 2018.
  16. Pelvic MRI for Guiding Treatment Decisions in Rectal Cancer. http://www.cancernetwork.com/oncology-journal/pelvic-mri-guiding-treatment-decisions-rectal-cancer . Last accessed July 20.
  17. Essential Items for Structured Reporting of Rectal Cancer MRI… Korean Journal of Radiology.  https://www.kjronline.org/DOIx.php?id=10.3348/kjr.2017.18.1.132 . Last accessed July 20, 2018.
  18. Prediction of KRAS Mutation in Rectal Cancer Using MRI. Anticancer Research. http://ar.iiarjournals.org/content/36/9/4799.abstract. Last accessed July 20, 2018.
  19. MRI Staging of Colorectal Cancer. The Association of Colombian Gastroenterologists.  http://www.scielo.org.co/pdf/rcg/v31n3/en_v31n3a11.pdf. Last accessed July 20, 2018.
  20. MRI for evaluation of treatment response in rectal cancer. The British Institute of Radiology. https://www.birpublications.org/doi/full/10.1259/bjr.20150964 . Last accessed July 20, 2018.
  21. MRI of Rectal Cancer: An Overview and Update on Recent Advances. American Journal of Radiology. https://www.ajronline.org/doi/full/10.2214/AJR.14.14201. Last accessed September 19, 2018.