Individual cancers have risk factors associated with them and many cancer types share the same risk factors. For example, if a person smokes they are not only at risk of developing lung cancer but they are also more susceptible to several other cancer types, such as mouth and bladder cancer.

Genetics also play a role when it comes to cancer risk factors. However, research suggests that only 5% to 10% of cancer diagnoses can be attributed to an inherited gene mutation – meaning that, in the majority of cases, cancer occurs as a result of environmental and lifestyle factors.

Many people worry that they are at a higher risk of developing cancer if a close family member has been diagnosed. So here we take a closer look at the relationship between cancer and genetics.

Cancer and Genetics

We are all born with a set of genes that are handed down by our parents and which describe our physical and biological characteristics. We inherit physical features such as eye color and body shape. We can also inherit an increased predisposition to certain medical conditions.

Genes play an essential role in the development of cancer. In the vast majority of cases, a mutation occurs in the cell’s DNA which creates a cancerous growth or tumor. This is called somatic mutation and arises, for example, as a natural consequence of ageing.

These types of mutation are particular to the individual and cannot be passed on to children.

In some circumstances, however, we see hereditary cancer where a predisposition to a certain condition can be passed from one parent to a child through the genes.

A mother or father passing on the mutated gene may not have the disease themselves. The presence of such a mutation, however, increases the likelihood of cancer developing in later life for their child.

Which Cancers are Hereditary?

In recent years, researchers have found several genes that may influence whether someone develops certain cancers or not. According to The Canadian Cancer Society, a genetic component has been discovered for the following cancer types:

  • adrenal gland cancer
  • bone cancer
  • brain and spinal cord cancers
  • breast cancer
  • colorectal cancer
  • eye cancer
  • fallopian tube cancer
  • kidney cancer
  • leukemia and lymphoma
  • hepatoblastoma
  • neuroblastoma
  • neuroendocrine tumours
  • oropharyngeal cancer
  • ovarian cancer
  • pancreatic cancer
  • parathyroid gland cancer
  • pituitary gland cancer
  • prostate cancer
  • rhabdomyosarcoma
  • skin cancer
  • small intestine cancer
  • soft tissue sarcoma
  • stomach cancer
  • testicular cancer
  • thyroid cancer
  • uterine cancer

Cancer and genetics is a complicated topic. Some genetic mutations increase the likelihood of several different diseases occurring.

For example:

  • A mutated gene that increases the risk of breast cancer can also mean a person is more vulnerable to ovarian cancer.
  • The effect of a gene mutation can diminish over generations.
  • The combination of genes from both parents can have a significant impact on how vulnerable an individual is of developing the disease.

Genetic Counselling and Testing

Saliva sample
A saliva sample can be used in the process of genetic testing

The idea that some forms of the disease can be passed down through family members has led to an increased focus on hereditary cancer in recent years. Genetic counselling and testing have become more popular and can help clarify if there is a familial connection.

First, it’s important to understand that cancer is very common. 1 in 3 people in the US will get some form of cancer and only in a small number of cases is there a genetic component. Just because there is an incidence of cancer in a family doesn’t necessarily mean that a mutated gene is being handed down through the generations.

Other ingrained environmental factors such as smoking, drinking and general health and wellbeing within the family unit may be the driving influence. However, certain factors may suggest that there is a genetic component involved.

These include:

  • A particular type of cancer occurring in the family. This is especially pertinent if the cancer is rare.
  • Cancers occurring at younger ages than would normally be expected.
  • A person developing more than one type of cancer.
  • Cancer occurring across numerous generations.

Another indicator would be if cancer occurs in two organs of a pair at the same time (for example, both lungs or both eyes).

The first step in genetic counselling and testing involves taking a complete history of the family to see if there may be a relationship that is due to something other than chance or environmental factors.

For example, if the cancer is occurring on one side of the family only, it can give a clear indication that there is a genetic relationship at work.

The testing itself is relatively simple and painless and involves either giving a blood sample or saliva and can give the individual a more precise determination whether they have a particular gene mutation.

Genetic counselling and testing do not mean that an individual will develop or not develop the disease. It’s purely a way of determining if that risk factor is there. What it does mean is that an individual can make decisions about life choices and future medical care.

On Going Research

We are only just beginning to understand the link between genetics and cancer and there is still much to be uncovered. While most cancers occur by chance mutations, certain risk factors increase our vulnerability. Understanding if there is a genetic link can help us make mitigating decisions about personal health choices.