Pathobiology

Colorectal lesions may be cancerous or noncancerous polyps. Some polyps that begin noncancerous may still hold malignant potential and become cancerous (adenomas and serrated polyps).1,2
~70% OF CRC DEVELOPS FROM ADENOMAS3

The evolution of colorectal adenoma to early-stage CRC typically takes more than 10 years, providing an important opportunity for screening and early detection3,4

Basic Anatomy of Colon and Rectum

Basic Anatomy of Colon and Rectum
Source: Shutterstock.com
The colon is a muscular tube about 5 feet long (1.5 meters) that is divided into 4 sections:1

 

  • Ascending
  • Transverse
  • Descending
  • Sigmoid
  • Rectum is the final 6 inches (15 cm) of the large intestine

Understanding Colon Pathology

Flowchart of Colorectal polyp physiology

Stages Of Colorectal Cancer

Image of anatomical split colon with tumors
  • CRC usually begins as a polyp1
  • When a polyp progresses to cancer, it can grow into the wall of the colon/rectum (local)1
  • It may invade lymph vessels and spread to nearby lymph nodes (regional)1
  • Cancer cells may also be carried via blood vessels to other organs such as the liver or lung (distant)1
  • Exfoliation of cellular material occurs in advanced adenoma and CRC that is not seen in normal mucosa5

Right-Sided Vs. Left-Sided CRC6,8

Infographic of left and right sided CRC

 Characteristic features of CRC by anatomic subsite6

RIGHT-SIDED (PROXIMAL) CRC LEFT-SIDED (DISTAL) CRC
Mucinous adenocarcinomas, sessile serrated adenomas Tubular, villous adenocarcinomas
Flat like morphology Polypoid like morphology
MSI-high and mismatch repair deficient tumors CIN-high tumors
Highly immunogenic, high T cell infiltration Low immunogenic
Metastases in peritoneal region Liver and lung metastases
More common in >50 y.o. More common in <50 y.o.
Predominantly occur in females Predominantly occurs in males
Better prognosis at early stages (stage I and II) Better prognosis at late stages (stage III and IV)

References

American Cancer Society. Colorectal cancer facts & figures 2020-2022. Atlanta: American Cancer Society; 2020.

Shussman N, Wexner SD. Colorectal polyps and polyposis syndromes. Gastroenterol Rep. 2014;2(1):1-15.

Rex DK, Boland CR, Dominitz JA, et al. Colorectal cancer screening: recommendations for physicians and patients from the U.S. Multi-Society Task Force on Colorectal Cancer. Am J Gastroenterol. 2017;112(7):1016-1030.

Winawer SJ, Fletcher RH, Miller L, et al. Colorectal cancer screening: clinical guidelines and rationale. Gastroenterol. 1997;112:594-642.

Geenen DJ, et al. A 3-year observational study of persons with a negative colonoscopy and positive multi-target stool DNA test, 2017. Poster presented at: Digestive Disease Week (DDW); 6-9 May 2017; Chicago, IL.

Baran B, Mert Ozupek N, Yerli Tetik N, et al. Difference between left-sided and right-sided colorectal cancer: a focused review of literature. Gastroenterol Res. 2018;11(4):264-273.

Bylsma LC, Gillezeau C, Garawin TA, et al. Prevalence of RAS and BRAF mutations in metastatic colorectal cancer patients by tumor sidedness: a systematic review and meta-analysis. Cancer Med. 2020;9(3):1044-1057.

8 Siegel RL, Miller KD, Fuchs HE, et al. Cancer statistics, 2022. CA Cancer J Clin. 2022;72:7-33.

Last Updated: 3/1/2022