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

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
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

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)


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