Genes and How They Work

All cells in the body contain genetic information that directs growth, development and normal bodily functions. This information is stored in DNA (deoxyribonucleic acid), which is organised into structures called chromosomes located within the cell nucleus.

Most human cells contain 46 chromosomes, arranged in 23 pairs. One chromosome of each pair is inherited from the mother and the other from the father. Chromosomes contain thousands of genes, which act as instructions for producing proteins and regulating the body's biological processes.

Genes influence inherited characteristics such as eye colour and certain physical traits, but most characteristics, as well as the risk of developing diseases, result from the interaction between genetic factors and environmental or lifestyle influences.

DNA is composed of a sequence of four chemical bases:

  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)

The combination of these bases constitutes the genetic code needed for the normal functioning of cells.

Genes and Cancer

Cancer develops as a consequence of accumulated genetic and molecular alterations within cells. Certain genes play essential roles in:

  • Controlling cell growth and division.
  • Repairing DNA damage.
  • Eliminating ageing or abnormal cells through programmed cell death (apoptosis).
  • Maintaining genetic stability.

When these genes undergo alterations or mutations, cells may lose their normal control mechanisms and begin to multiply uncontrollably, increasing the risk of cancer development.

Two main types of genetic mutations are recognised:

Acquired (Somatic) Mutations

These are the most common type of mutation and develop during a person's lifetime in specific cells of the body.

They may arise as a result of:

  • Natural errors during cell division.
  • Tobacco exposure.
  • Ultraviolet radiation.
  • Ionising radiation.
  • Certain chemical substances.
  • Some inflammatory or infectious processes.

These mutations:

  • Are not present at birth.
  • Cannot be passed on to children.
  • Are responsible for the vast majority of cancers.

Tumours that arise primarily as a result of acquired mutations are known as sporadic cancers.

Inherited (Germline) Mutations

Inherited mutations are present from birth because they are passed down through the egg or sperm.

These genetic alterations can increase a person's predisposition to develop certain types of cancer and are associated with the so-called hereditary cancer predisposition syndromes.

It is important to understand that inheriting a mutation does not mean that a person will definitely develop cancer. It means that their risk is higher than that of the general population. The eventual risk also depends on environmental, hormonal and lifestyle-related factors.

What Proportion of Cancers Are Hereditary?

Current evidence suggests that approximately 5% to 10% of all cancers are caused by identifiable inherited genetic mutations. Most cancers are not hereditary and result from a combination of factors acquired throughout life.

Main Hereditary Cancer Syndromes

Some of the best-known hereditary cancer syndromes include:

BRCA1 and BRCA2 Mutations

These mutations are associated with an increased risk of:

  • Breast cancer.
  • Ovarian cancer.
  • Prostate cancer.
  • Pancreatic cancer.

Lynch Syndrome

Lynch syndrome is the most common inherited cause of hereditary colorectal cancer and is also associated with an increased risk of:

  • Endometrial cancer.
  • Ovarian cancer.
  • Gastric cancer.
  • Other gastrointestinal and urinary tract cancers.

Familial Adenomatous Polyposis (FAP)

This condition is characterised by the development of numerous polyps in the colon and a very high risk of colorectal cancer if appropriate surveillance and treatment are not provided.

When Should Hereditary Cancer Be Suspected?

Referral for genetic counselling may be appropriate in circumstances such as:

  • Several family members affected by the same type of cancer.
  • Cancer diagnosed at an unusually young age.
  • A person with multiple primary cancers.
  • Repeated cases of breast, ovarian, prostate or colorectal cancer within the same family.
  • A known inherited genetic mutation in a family member.

In these situations, healthcare professionals may recommend a specialised assessment that includes genetic counselling and, where appropriate, molecular genetic testing.

Genetics and Personalised Medicine

Current international guidelines recommend the use of genetic testing and biomarker analysis when clinically indicated, both to identify inherited cancer predisposition and to guide personalised treatment strategies.

This approach forms part of what is known as precision oncology, which allows prevention, surveillance and treatment to be tailored to the specific characteristics of each patient and their tumour.