Familial, Hereditary and Sporadic: Frequently Confused Concepts in Cancer

One of the most confusing issues about cancer is viewing all cancer as a hereditary disease. It must be emphasized that cancer is a genetic disease at the cellular level. As damage accumulates in genes responsible for normal bodily functions, our cells begin to multiply uncontrollably and pass these defective genes to daughter cells. However, this does not mean that all cancers are hereditary diseases.

Studies conducted after mapping the human genome found that most damage causing cancer ( mutations ) occurs in body cells, that is, somatic cells. These mutations are called somatic mutations. In other words, this damage does not pass to offspring through inheritance. However, although uncommon, mutations occurring in reproductive cells pass to offspring and increase cancer risk. These mutations are called germline / hereditary mutations.

Genetically, cancer is divided into 3 groups

1. Sporadic cancers
2. Familial cancers
3. Hereditary cancers

Sporadic cancers

Sporadic cancers environment and aging arise through their effects and account for approximately 80 percent of all cancers . In other words, they are cancers resulting from accumulated DNA damage over time. Looking at the characteristics of sporadic cancers, we see that these cancers mostly arise at older ages. The likelihood of finding a hereditary mutation in genetic testing for these cancers is very low. Even if multiple cancer cases occur in a cancer patient’s family, this does not indicate hereditary transmission. Today, we know that sporadic cancers can largely be prevented through lifestyle changes.

Familial cancers

They are often confused with hereditary cancers, but their underlying causes differ. They involve frequent occurrence of the same cancer type in family members. For example, suppose breast cancers occur in an individual’s family but testing finds no “inherited gene defects” increasing the individual’s breast cancer risk. If this individual develops cancer, it is considered in the familial cancer category. A person’s overall genetic structure, environment and lifestyle determine the risk of familial cancers. Hereditary cancer syndromes are not seen in this type of cancer. They usually arise in middle age. Epigenetics (inheritance above genes) is the name of mechanisms thought to influence this type of cancer. Familial cancers occur at a rate of 10-15 percent. A good example of genetic predisposition is “why smoking causes cancer in some people but not others.” DNA repair genes may not function as actively in these families as in others. You can read our explanation and Professor Aziz Sancar’s work here .

Hereditary cancers

Certain specific cancer types arise in offspring as a result of inherited damage (mutations) in particular genes. They occur at younger ages than sporadic cancers. These cancers are rare and generally multifocal (cancer in more than one organ or multiple foci in the same organ). First-degree relatives of people carrying damaged genes have a 50 percent risk of having the same damage. Hereditary cancers occur at a rate of 5-10 percent.

- You may be interested in: Hereditary cancers and their genes

In summary

Cancer is a disease beginning genetically in a single cell. In sporadic cases, genetic changes usually occur in oncogenes in a somatic cell at any age, while in hereditary cases this change is present in “germline” tumor suppressor genes. Tumor suppressor genes encode proteins controlling the cell cycle or providing DNA repair. Mutations in this gene group cause additional mutations to accumulate in the cell and genetic instability , playing a role in carcinogenesis (cancer formation) and creating a genetic predisposition to cancer in the individual. Mutations in these genes have an autosomal recessive effect but clinically appear like a dominant inheritance pattern. Occurrence of the same cancer type in a family is defined as hereditary cancer, while different cancer types are defined as a “cancer family” or “familial cancer.”

Genetics in cancer is a concept gaining importance in recent years. Genes influencing cancer are discovered every day and used to develop tests for early cancer diagnosis. Understanding cancer’s genetic structure will enable development of gene therapy targeting the reason cancer arises.

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