Is Cancer Hereditary? Understanding Hereditary Cancer Risk

Medically reviewed by Dr Johann Tang, Senior Consultant Radiation Oncologist

Key Takeaways

• Cancer is not necessarily always hereditary. Only 5–10% of cancers are caused by inherited gene mutations.
• Most cancers arise from acquired mutations related to ageing, environment, and lifestyle.
• Understanding the link between genetic mutations and cancer risk supports timely screening and personalised care.
• A doctor can assess your family history and advise whether cancer may be hereditary, while identifying the need for genetic testing or earlier screenings.

Introduction

A cancer diagnosis within the family often raises understandable concerns about personal risk. Many individuals wonder whether cancer is hereditary and whether other family members could also be affected. While most cancers are not hereditary, understanding the role of genetics can help guide appropriate screening, surveillance, and medical decision-making.

How Cancer Develops: The Role of Genes and Mutations

Genes contain the instructions that regulate how cells grow, divide, and repair DNA damage. Cancer develops when mutations disrupt these normal cellular processes, allowing abnormal cells to grow uncontrollably.

Mutations generally fall into two categories:

Inherited Mutations

Inherited mutations are present from birth and passed from parent to child. These mutations exist in nearly every cell of the body and may increase an individual’s susceptibility to certain cancers.

Acquired Mutations

Acquired mutations develop over time as a result of ageing, environmental exposures, lifestyle factors, or random cellular changes. These mutations are far more common and account for the majority of cancers.

Importantly, inheriting a cancer-related mutation does not mean cancer will definitely develop. Rather, it increases the likelihood of cancer occurring compared to the general population.

Most Cancers Are Not Hereditary

Although cancer can occur within families, only a small proportion of cancers are caused by inherited genetic mutations. Broadly, cancers can be classified into three groups:

Hereditary Cancers (Approximately 5–10%)

Hereditary cancers are associated with inherited pathogenic variants in specific genes that substantially increase cancer risk. These cancers often present at younger ages, may affect multiple relatives across generations, and can involve characteristic patterns of disease.

Familial Cancers (Approximately 15–20%)

Familial cancers tend to cluster within families without a clearly identifiable single-gene cause. Shared environmental influences, lifestyle factors, and the combined effect of multiple low-risk genetic variants may all contribute.

Sporadic Cancers (Approximately 70–80%)

Sporadic cancers are the most common type of cancer. They arise from acquired mutations that accumulate over time and are typically unrelated to inherited genetic risk.

In many cases, a single cancer diagnosis in an older relative is more likely to represent a sporadic cancer rather than an inherited cancer syndrome.

Common Hereditary Cancer Syndromes

1. Hereditary Breast and Ovarian Cancer (HBOC) Syndrome

Hereditary Breast and Ovarian Cancer syndrome is most commonly associated with pathogenic variants in the BRCA1 and BRCA2 genes. These genes normally help repair damaged DNA and maintain normal cell function. When they do not function properly, the risk of several cancers increases.

Associated cancers may include:

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

Population studies in Singapore suggest that pathogenic BRCA1 or BRCA2 variants may be present in approximately 1 in 150 individuals. Individuals with these mutations may benefit from earlier screening, enhanced surveillance, and preventive risk-reduction strategies.

2. Lynch Syndrome (Hereditary Non-Polyposis Colorectal Cancer)

Lynch syndrome is an inherited condition caused by mutations in DNA mismatch repair genes, including MLH1, MSH2, MSH6, and PMS2. These mutations impair the body’s ability to correct DNA replication errors, increasing the risk of several cancers.

Associated cancers include:

• Colorectal cancer
• Endometrial cancer
• Stomach cancer
• Ovarian cancer
• Urinary tract cancers

Individuals with Lynch syndrome are often advised to begin colonoscopy screening in early adulthood, with surveillance performed at more frequent intervals than in the general population.

When Should Hereditary Cancer Risk Be Considered?

A strong family history of cancer may suggest the possibility of an inherited cancer syndrome. However, it is important to note that having relatives with cancer does not necessarily mean a hereditary condition is present.

You may wish to seek medical advice if you notice:

• The same type of cancer affecting multiple close relatives
• Cancer occurring at younger-than-expected ages
• One individual developing multiple primary cancers
• Rare cancers, such as male breast cancer
• A known hereditary cancer mutation within the family

In such situations, referral for genetic counselling and assessment may be appropriate.

Genetic Testing and Counselling

Genetic testing is not routinely recommended for everyone. It is generally considered when personal or family history suggests an increased likelihood of an inherited cancer syndrome.

Testing may be recommended for individuals with:

• Strong or suggestive family history patterns
• Relatives with confirmed BRCA or Lynch syndrome mutations
• Personal cancer diagnoses meeting established testing criteria

Genetic testing is typically accompanied by genetic counselling to help individuals understand the implications of test results for both themselves and their family members.

The Importance of Personalised Risk Assessment

Understanding whether cancer is hereditary can help guide decisions regarding cancer screening, surveillance, and long-term health planning. For individuals already diagnosed with cancer, genetic information may also influence treatment considerations and future risk management.

A personalised assessment of your medical and family history allows a cancer doctor to determine whether further evaluation, earlier screening, or genetic testing may be appropriate.

Seeking Professional Guidance

If you have concerns regarding inherited cancer risk or would like guidance on appropriate cancer screening strategies, consulting a qualified cancer specialist in Singapore can help clarify your options.

Dr Johann Tang provides assessment and guidance on cancer screening, hereditary cancer risk evaluation, and the role of radiation therapy in cancer management, including prostate cancer treatment and other oncological conditions.

Book an appointment to discuss your concerns and explore the most appropriate next steps for your care.