Colon cancer can be hereditary, which means it passes from generation to generation in families. It is also genetic, meaning it develops because of an accumulation of genetic changes.

Hereditary cancers, including hereditary colon cancer, are genetic. However, not all genetic cancers are hereditary. Sometimes a person develops changes during their lifetime due to exposure to environmental factors that trigger genetic mutations.

For example, tobacco, alcohol, and red or processed meat may increase the risk of genetic mutations that cause colon cancer.

About 1 in 30 cases of colon cancer are in people with a genetically inherited condition called Lynch syndrome. Doctors also call this hereditary nonpolyposis colorectal cancer.

Cancer, including colon cancer, develops because cells grow out of control. This often occurs when genes that prevent excessive cell growth or control the rate of cell growth develop mutations. The mutations can be hereditary or due to environmental factors.

Read on to learn more about the hereditary nature of colon cancer, including the genetic factors and some other causes of colon cancer.

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All cancers are genetic because changes in genes cause cells to grow out of control, leading to the disease. However, genetic does not mean hereditary.

Hereditary cancers are cancers that pass from generation to generation via genes. These cancers comprise only a small portion of colon cancers.

One of the most studied genetic forms of colon cancer is Lynch syndrome, which is also the most common.

People with Lynch syndrome mutations have a lifetime risk of colon cancer as high as 80%. Females with Lynch syndrome have a 60% lifetime risk of endometrial cancer. They may also develop other cancers, such as:

People with a family history of colon cancer are more likely to carry genes that increase the risk of cancer. This may mean they develop colon cancer at an earlier age. Doctors may recommend earlier and more frequent screenings, genetic counseling, and using colonoscopies to test for cancer instead of other, less sensitive tests.

However, not all family cases of colon cancer are hereditary. Some environmental risk factors, such as obesity, alcohol, and tobacco, may be more common according to a person’s family history. For example, a family might often eat red meat together, increasing their collective and individual risk of colon cancer.

Most cases of colon cancer are sporadic, which means there is no obvious hereditary cause, with around 20% due to familial clustering. These cases may spring from genetic factors, shared environmental exposures, or an interaction between the two. About 10% develop because of inherited syndromes such as Lynch syndrome.

While earlier research suggested that carriers of the BRCA1 and BRCA2 genes, which many people call the breast cancer genes, might have a higher risk of colon cancer, more recent research undermines that claim.

A 2020 meta-analysis that included nine prior studies and controlled for age, sex, and Ashkenazi heritage, found no increased risk among this group.

Lynch syndrome

People with Lynch syndrome inherit a mutation in the genes MLH1, MSH2, MSH6, or PMS2. Doctors call these mismatch repair genes because they repair incorrect pairings during the process of copying DNA. Without the ability to repair these copying errors, the risk of cancer increases.

A fifth genetic change, a group of deletions in the EPCAM gene, prevents the MSH2 gene from expressing, also causing Lynch syndrome.

Lynch syndrome causes about 5% of all colorectal cancers.

Additionally, a total of 10–15% of people with a colorectal cancer diagnosis carry other mutations that increase the risk of cancer.

About 70% of colon cancer cases are sporadic, meaning there is no clear genetic cause.

However, this disease develops because of the accumulation of genetic mutations that alter the colon lining. It usually takes 10 to 15 years for these mutations to occur at a frequent enough rate to lead to cancer.

A 2017 study that looked at genetic mutations in all cancers, not just colon cancer, found that about two-thirds of these mutations occurred because of random copying errors, not exposure to environmental factors.

However, environmental exposures, and the interaction between genetic risk factors and the environment, may increase the risk of colon cancer.

According to the Centers for Disease Control and Prevention (CDC), the main risk factors for colon cancer include:

  • getting older
  • inflammatory bowel disease
  • a sedentary lifestyle
  • a diet high in fat or processed meat
  • drinking alcohol
  • using tobacco
  • being obese or overweight

Colon cancer does not always cause symptoms. People with genetic or environmental risk factors for this disease should not assume they are cancer-free because they do not have symptoms. Instead, they should speak with a doctor about a suitable cancer screening schedule.

Some symptoms of colon cancer may include:

  • a bloody stool
  • a change in bowel habits
  • constipation
  • diarrhea
  • feeling unable to fully empty the bowels
  • unexplained abdominal pain, especially if it does not go away
  • unexplained weight loss

For people with Lynch syndrome or other genetic risk factors for colon cancer, prevention and early detection are important. A person may meet with a genetic counselor or doctor to discuss screening guidelines.

For cancer that has not spread outside of the colon, the main treatment method is surgical resection. This procedure involves removing the cancer by removing part of the colon. People with early stages of cancer do not need chemotherapy if this surgery is successful.

With more advanced cancers, a person may need chemotherapy. If the cancer spreads to other organs, this may also require additional surgeries to remove it.

The outlook for people with an early diagnosis of colon cancer is good. The American Cancer Society reports the following 5-year relative survival rates, which indicate the percentage of individuals who are alive 5 years following diagnosis:

  • localized cancer: 91%
  • regional cancer: 72%
  • distant or metastatic cancer: 14%
  • all stages combined: 64%

Despite these figures, colon cancer is the third leading cause of cancer death for males and females combined. And while rates have declined in general, the rate of colon cancer among people over the age of 50 years has increased.

Colon cancer is genetic, but not all cases of colon cancer spread through families. Instead, random changes in genes and mutations due to environmental factors may increase the risk of this type of cancer.

People with inherited family syndromes have a very high risk of developing colon cancer. A person who has several cases of colon cancer in their family should talk with a doctor or genetic counselor. If they test positive for a genetic syndrome, they may need more frequent and aggressive colon cancer screening.