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A Brief Overview of Cancer Genetics

Cancer is fundamentally a genetic condition. Although lifestyle and environmental factors can contribute, the disease primarily stems from genetic damage. Some people inherit mutations that increase their risk of developing cancer, while most mutations arise spontaneously.

Your genes provide the essential instructions for nearly every aspect of your body. You have between 20,000 and 25,000 genes organized into 23 pairs of chromosomes. Each gene plays a vital role in your biological makeup—specifically, your DNA.

In each of the roughly 37 trillion cells in your body, there are more than 2 meters (6 feet) of tightly packed DNA. This genetic material dictates how each type of cell functions, including when to grow, replicate, and die.

Cancer develops when this DNA code is damaged. In rare cases, these DNA mutations can be passed down through generations, resulting in patterns of cancer within families.

Keep reading to learn more about the factors that lead to cancer and how it can be inherited.

Is Cancer Genetic or Environmental?

To understand the origins of cancer, it’s crucial to recognize the different factors that can damage your DNA. Mutations may result from:

Environmental Factors: External influences such as UV radiation or exposure to harmful chemicals can damage DNA. Substances that cause DNA mutations and can lead to cancer are known as carcinogens.

Metabolism: This process converts food into energy for your cells. During metabolism, DNA damage can occur, resulting in an accumulation of genetic errors over time. It’s estimated that this happens around 70,000 times each day.

Spontaneous Mutations: Throughout your life, your cells undergo trillions of divisions. While this process is generally accurate, spontaneous errors (mutations) can occur, typically once in every 100,000 to 100 million divisions.

Usually, your body can correct these errors. Even when it doesn’t, most mutations don’t lead to significant changes. However, if a mutation affects specific genes, it can potentially result in cancer.

Research from 2017 indicated that about two-thirds of cancers are due to random gene alterations during cell replication.

What Percentage of Cancer is Genetic versus Environmental?

All cancers are, by definition, genetic, as they result from DNA damage leading to mutations. However, if you’re asking about the proportion of cancer attributable purely to genetic factors versus environmental influences, the answer differs.

According to a 2017 study, only around 23% of all cancers can be linked to environmental factors. The rest arises from genetic factors, including inherited mutations or spontaneous DNA replication errors.

These proportions can vary depending on the cancer type. For example, the same study found that environmental factors contributed to less than 15% of prostate, brain, and breast cancers, whereas they accounted for over 60% of lung and skin cancers.

What Types of Genes Contribute to Cancer?

Cancer does not generally result from random mutations in any gene. Although your cells experience trillions of point mutations daily, most don’t lead to significant changes. However, mutations in specific types of genes can lead to cancer.

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Oncogenes

Proto-oncogenes are genes that normally promote healthy cell growth. A mutation can turn these into oncogenes, which cause cells to grow and divide uncontrollably when activated. Most mutations that lead to oncogene activation are not inherited.

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Tumor Suppressor Genes

Tumor suppressor genes normally regulate cell growth and division. A mutation that inactivates a tumor suppressor gene can result in uncontrolled cell division. Similar to oncogenes, mutations affecting tumor suppressor genes are usually not passed down.

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DNA Repair Genes

DNA repair genes are tasked with correcting errors that occur during DNA replication. If these genes are mutated, they may not effectively fix mistakes, potentially leading to cell death. Notable examples include the BRCA1 and BRCA2 genes; inherited mutations in these significantly raise the risk of breast and ovarian cancers.

Is Cancer Hereditary?

A hereditary condition is one that can be transmitted through generations. While this is partially true for cancer, it isn’t completely accurate. While some cancers can be hereditary, most cases are not.

Most cancers are categorized as somatic variants, which arise from DNA damage in somatic cells (any cells that aren't sperm or egg cells). These mutations cannot be inherited.

Conversely, about 5% to 10% of cancers are germline variants, originating from mutations in sperm or egg cells. These can be passed on to children, integrating into the DNA of every cell.

However, inheriting a mutation does not guarantee that the child will develop cancer; it simply increases their risk.

What Percentage of Cancer is Hereditary?

According to the National Cancer Institute, up to 10% of cancers are hereditary, meaning they involve inherited genetic mutations that elevate cancer risk.

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What Are Family Cancer Syndromes?

Inherited genetic mutations can manifest within families, resulting in conditions known as family cancer syndromes or hereditary cancer syndromes. These syndromes are relatively uncommon. In the U.S., one in three people will develop cancer, raising the likelihood of multiple family members being affected. Family cancer syndromes often have certain traits:

• The same type of cancer appears across several generations, especially if it is rare.

• Family members may develop cancer at an unusually young age.

• Some individuals may have multiple types of cancer.

• Cancer may occur in paired organs, such as both breasts or kidneys.

Examples of family cancer syndromes include:

• Familial Adenomatous Polyposis (FAP): Caused by an inherited mutation in the APC gene, increasing colorectal cancer risk.

• Hereditary Breast and Ovarian Cancer Syndrome (HBOC): Results from inherited mutations in BRCA1 or BRCA2 genes, raising risks for breast and ovarian cancers.

• Li-Fraumeni Syndrome (LFS): Caused by a mutation in the TP53 tumor suppressor gene, leading to a 70% to 90% risk of various cancers, including breast cancer and CNS tumors, depending on the individual’s sex assigned at birth.

• Cowden Syndrome: Caused by an inherited mutation in the PTEN gene, increasing risks for skin, breast, thyroid, and kidney cancers, among others.

• Lynch Syndrome: Affects one of five possible DNA repair genes, heightening risks for various cancers, including colorectal, stomach, and uterine cancers.

Familial vs. Hereditary Cancers

Certain cancers, such as breast and prostate cancer, often occur within families. However, not all familial cancers are due to inherited mutations or syndromes; some may arise from shared environmental influences.

Hereditary cancers tend to appear earlier in life, usually before age 50, and may involve rare cancers or multiple sites, such as both breast and ovarian cancers. They often manifest across several generations within a family.

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Which Types of Cancers Are Common in Families?

Common cancers that frequently occur in families due to genetic factors include:

• Breast

• Colorectal

• Stomach

• Prostate

• Pancreatic

• Ovarian

• Endometrial (uterine)

• Melanoma

Keep in mind that some cancers may be prevalent in families for reasons other than genetics, such as environmental or lifestyle influences. Some cancers are simply more common.

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How Likely Am I to Pass on Cancer to My Child?

If you have cancer caused by an inherited gene mutation, your child has a 50% chance of inheriting that mutation. However, this does not guarantee that your child will develop cancer; it merely indicates a higher risk.

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Can I Prevent Hereditary Cancer?

Latest technology like ECCT helps to prevent an inherited gene mutation by detecting the abnormal cells formation and prevent it from further development into abnormal cells, having such a mutation does not mean you will definitely develop cancer. It simply means your risk is increased.

You can also help lower your risk of cancer by minimizing environmental factors that contribute to its development. Regular screenings can also facilitate early detection if cancer does occur.

Learn more about lifestyle and dietary changes that may help reduce cancer risk.

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What Is Genetic Testing for Cancer?

If you suspect that an inherited cancer may be present in your family, you might consider genetic testing. This typically involves taking a blood, saliva, or tissue sample for analysis in a lab. The results can determine whether you carry a gene mutation that increases your cancer risk.

It’s important to understand that genetic testing does not predict whether you currently have or will develop cancer; it merely assesses your risk.

However, genetic testing might not be appropriate for everyone. Consulting a genetic counselor can provide valuable insights into the advantages and disadvantages of testing before you decide.

Benefits of Genetic Testing for Cancer

• A positive result may prompt more frequent and earlier screenings.

• A positive result may encourage preventive measures.

• A negative result can relieve anxiety.

• It can help you understand the risk of passing the gene to your children.

Drawbacks of Genetic Testing for Cancer

• A positive result may increase anxiety.

• It might lead to unnecessary further testing.

• Privacy concerns may arise, particularly regarding issues of paternity or adoption.

• The cost of testing can be high.

Cancer operates on a genetic level, categorizing it as a genetic disease. However, this does not imply that it is hereditary.

Only about 5% to 10% of cancers are hereditary. Even inheriting a mutation linked to cancer does not guarantee cancer development; it simply raises the risk significantly.

Some cancers, like breast and prostate cancer, are more likely to occur in families, while others, like brain and lung cancer, generally have different causes.

If cancer is common in your family, consider genetic testing and counseling to enhance your understanding of your risk.