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Colorectal cancer and genetics

Genetics is an essential factor in the development of colorectal cancer. A large number of genes may influence each person’s predisposition to develop this disease at some point in his or their life. In addition, these genes may also be involved in developing other types of cancer.

If you want to know what colorectal cancer is, its primary symptoms, how it’s diagnosed, the risk factors for developing the disease, and the relationship between genetics and its development, keep reading.


What is colorectal cancer?

Colorectal cancer is cancer that begins with the uncontrolled mutation of cells in the colon or rectum. For this reason, this type of cancer is also called rectal or colon cancer. However, they are usually grouped under a single name because of the many common characteristics of both types of tumors.

In general, this type of cancer begins with forming of a polyp in some area of the colorectal tissue. Some polyps may develop into cancer over the years, but others will remain benign tumors. This transformation depends, among others, on genetic factors [1].

However, although colorectal cancer with polyps is the most common, it can also occur without them. This is the case of people with long-standing inflammatory bowel diseases, such as chronic ulcerative colitis and Crohn’sCrohn’s colitis. In addition, people with Lynch syndrome have a higher chance of developing colorectal cancer before age 50, which is called hereditary non-polyposis colorectal cancer. 

In this blog, we will focus on colorectal cancer in the presence of polyps. 


Symptoms of colorectal cancer

At the beginning of the disease, it’s possible that neither colorectal cancer nor the polyps that can generate it cause symptoms. This is why, in this particular type of cancer, early detection by specific tests is so important [2]. In the case of any sign or symptom of colorectal cancer, these are usually:

  • Permanent change in bowel habits such as diarrhea, constipation, feeling that the bowel does not empty when defecating, or stool that is thinner in appearance or shaped differently than usual.
  • Blood in the stool (may manifest with an almost black color of the stool).
  • Frequent pain or discomfort, bloating, the feeling of fullness or cramping.
  • Weight loss for no reason.

How is the diagnosis of colorectal cancer made?

In some countries, there’s a colorectal cancer prevention program. The general population over a certain age, usually 50, is screened for blood in the stool. The aim is to achieve an early diagnosis of the disease to detect it in the absence of symptoms.

If this test gives an adverse result, if there are any symptoms related to colorectal cancer, or if the family history makes it advisable, there are a series of tests for a more accurate diagnosis. These are [1]:

  • Colonoscopy: observing the inside of the colon and rectum with a small camera.
  • Computed tomography colonography (CT or CAT): method still under investigation in some centers.
  • Sigmoidoscopy: similar to colonoscopy but with a smaller scope of vision.
  • Double-contrast barium enema: usually used as an alternative to colonoscopy, but the probability of detecting precancerous polyps is lower.
  • Stool DNA testing analyzes DNA changes that cause polyps and cancer.


Risk factors for colorectal cancer

Although the causes of colorectal cancer are not known precisely, several risk factors appear to increase the likelihood of developing the disease. Among them are [1]:

  • Age: there is an increased risk with age, higher after 50.
  • Ancestry: there is a greater probability of developing colorectal cancer in people with African ancestry.
  • Sex: biological men have a slightly higher risk.
  • Inflammatory bowel disease.
  • Adenomatous polyps (adenomas).
  • Sedentary lifestyle and obesity 
  • Smoking.
  • Diet: consumption of red and processed meats increases the risk.
  • Family history: the risk can even double.
  • Rare hereditary conditions: such as different types of polyposis or syndromes.
colorectal cancer genetics

Is colorectal cancer hereditary?

Genetic factors related to mutations in some genes can directly influence colorectal cancer. Inactivation, for example, of the APC gene, is one of the main signs, at the genetic level, for early detection of sporadic colon cancer. It’s commonly thought that more than 85% of colon tumors are associated with somatic mutations in this gene [3].

Almost all mutations in the APC gene cause a disease called familial adenomatous polyposis (FAP). This disease increases the risk of colorectal cancer and other types of cancer, such as pancreatic cancer [4].


24Genetics and the detection of mutations associated with colorectal cancer

Aside from colorectal cancer screening tests, DNA analysis can also provide information about genetic predisposition to colorectal cancer. For example, with the 24Genetics health test, you will know your propensity to suffer from colorectal cancer and many other diseases by analyzing mutations in the genes involved in their development or different methodologies.

Bet on prevention to achieve success in the early detection and treatment of a wide variety of types of cancer and non-oncological diseases of hereditary origin. Get your DNA test now on our website and learn all the information your genes hold!



[1] Colorectal cancer – American Society of Clinical Oncology – Peer-reviewed by the Cancer.Net Editorial Board [revised Jan. 2021; accessed Mar. 2023] Available at: https://www.cancer.net/es/tipos-de-cancer/c%C3%A1ncer-colorrectal

[2] Colorectal cancer What are the symptoms? – Division of Cancer Prevention and Control, Centers for Disease Control and Prevention [reviewed Feb. 2023 – accessed Mar. 2023] Available at: https://www.cdc.gov/spanish/cancer/colorectal/basic_info/symptoms.htm

[3] Chung DC. The genetic basis of colorectal cancer: insights into critical pathways of tumorigenesis. Gastroenterology 2000; 119: 854-65. [reviewed Jul. 2005; accessed Mar. 2023] Available from: https://www.sciencedirect.com/science/article/abs/pii/S0016508500081622

[4] Information on APC gene mutations – Memorial Sloan Kettering Cancer Center [updated Jul. 2021; revised Mar. 2023] Available from: https://www.mskcc.org/es/cancer-care/patient-education/about-mutations-apc-gene

Written by Debora Pino García


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