Cancer is a complex disease, and its origins are often misunderstood. A common question is whether cancer is always genetic. While genes can play a role, the vast majority of cancers are not directly inherited. Instead, cancer typically arises from a combination of acquired genetic changes and environmental exposures.
When Genes Play a Role
In some instances, an individual can inherit a predisposition to cancer through specific gene changes. These are known as germline mutations, present from birth in every cell. Such inherited mutations account for a smaller proportion of all cancers, typically around 5% to 10%.
These inherited changes increase a person’s risk of developing certain cancers, though they do not guarantee cancer will occur. For example, mutations in the BRCA1 and BRCA2 genes are inherited predispositions that increase the risk of breast and ovarian cancers. If a parent carries such a gene change, each child has a 50% chance of inheriting it.
Another example is Lynch syndrome, caused by inherited mutations in specific DNA mismatch repair genes. Individuals with Lynch syndrome have an increased risk of developing colorectal cancer, endometrial cancer, and other cancers, often at a younger age. These inherited cancer syndromes highlight situations where genetic factors directly contribute to increased cancer risk.
When Cancer is Not Inherited
The majority of cancers, around 90% to 95%, are considered sporadic. These cancers result from acquired, or somatic, mutations that occur in cells during a person’s lifetime. These mutations accumulate over time and are confined to the specific cells that become cancerous.
Various external factors can lead to these acquired genetic changes. Exposure to ultraviolet (UV) radiation from the sun, for instance, can damage DNA in skin cells, leading to mutations that cause skin cancers. Harmful chemicals in tobacco smoke are another major cause, inducing mutations in lung cells and other tissues.
Certain viruses, like the human papillomavirus (HPV), can cause acquired mutations that lead to cancer. Persistent high-risk HPV infections can lead to changes in cells that, over time, may progress to cancers such as cervical, anal, and some head and neck cancers. Errors can also occur spontaneously during normal DNA replication as cells divide, contributing to the accumulation of mutations. Chronic inflammation, often due to persistent infections or irritants, can create an environment that promotes DNA damage and genetic instability, increasing cancer risk.
How Genes and Environment Interact
Cancer development often involves a complex interplay between an individual’s genetic makeup and their environmental exposures. Even in cases of sporadic cancer, a person’s inherited genetic variations can influence how their body responds to environmental carcinogens. Some individuals may possess genetic differences that affect their ability to repair DNA damage or detoxify harmful substances.
This means that while a person might not have a specific inherited cancer syndrome, their unique genetic background could make them more susceptible to the effects of certain environmental risk factors. For example, variations in genes involved in DNA repair pathways can impact how effectively the body corrects damage caused by exposure to toxins.
Beyond direct DNA sequence changes, environmental factors can also influence epigenetics, modifications to gene expression without altering the DNA sequence itself. Diet, lifestyle, and chemical exposures can induce epigenetic changes, affecting how genes are turned on or off, and potentially contributing to cancer development. This intricate relationship underscores that cancer is rarely due to a single cause, but rather a combination of inherited predispositions and lifetime exposures.
Implications for Personal Health
Understanding the varied origins of cancer has important implications for personal health. While a small percentage of cancers are linked to inherited gene changes, many more arise from acquired mutations influenced by lifestyle and environmental factors. Recognizing one’s family history of cancer is a valuable step in assessing personal risk, as it can indicate a potential inherited predisposition.
However, family history is only one piece of the puzzle. Awareness of general risk factors, such as exposure to tobacco, excessive sun, and certain infections, is also important. Knowing that most cancers are not inherited empowers individuals to focus on broader health choices that can influence their overall cancer risk. This balanced perspective helps in making informed decisions about personal health.