Certain types of cancer can run in families via the genes. Cancer may be inherited through abnormal diseased genes which are found in one generation and passed on to the next one. Despite this fact, not more than 5% to 10% of all cancer cases are inherited.

Cancer can be caused by abnormal genes on damaged DNA. DNA is the instructions storage of the cell, which contains millions of genes; each of these genes carries certain instructions for the cell to produce a certain type of protein that has its own function in the cell. In fact, our genes control everything in our bodies including color of hair and eyes, height, and shape of our bodies, etc.

Medically, if any abnormal change occurs in a gene, it’s called a mutation. Genetically, there are two types of mutations:

  1. Inherited mutations are those mutations which are passed from parents to children. As they are inherited in the first place, they are in every single cell of the body.
  2. Acquired mutations or somatic mutations are those mutations which occur accidentally during life. They are much more common and they are present in one cell only, not in all the body cells like inherited mutations.

Carried genes in the DNA are in special arrangement of strands; those strands are known as chromosomes. We, as human beings, have 23 pairs of chromosomes in every single cell; one pair from the mother and the other pair from the father. Each chromosome contains thousands of genes which are inherited from one of the parents.

The inherited gene mutation is inside the egg of the mother or sperm of the father. When the egg is fertilized by the sperm, one main embryo cell is created called a zygote. The zygote divides and creates a fetus which later becomes an infant and then becomes an adult. The one-cell Zygote formed from the mother's egg and sperm from the father is the main source of each cell.

The acquired gene mutation, also called somatic, is not inherent in the zygote or sperm. As the name suggests, it is acquired later. The acquired gene mutation occurs in a certain cell, and then it passes to another cell during the process of cell division. Since inherent gene mutation is not present in the egg or sperm, it cannot pass that onto next generation. Somatic gene mutations are more common compared to inherited gene mutations. The vast majority of cancers develop as result of acquired gene mutations.

Role of genes in cancer etiology

Genes play two important roles in cancer etiology:

  1. Oncogenes: Oncogenes are simply abnormal mutated genes which arise from normal genes, named proto-oncogenes. Proto-oncogenes are those genes which control the type of cell and its growth rate. If a mutation occurs in proto-oncogene, it will become oncogene. Oncogene will stimulate the uncontrolled growth of the cell leading to the development of cancer.
  2. Tumor suppressor genes: Tumor suppressor genes are normal genes which work to reduce the speed of cell division and to repair any damage in the DNA. When there is a problem in the tumor suppressor gene, the cells will grow indefinitely and without control leading to the development of cancer.

This balance between proto-oncogenes and tumor suppressor genes maintains the normal growth of the cells within the normal ranges. Basically, cancer can occur if oncogenes are activated due to a mutation in the normal proto-oncogenes or if the tumor suppressor genes are deactivated.

Most of people are born with healthy genes, but the chance of having mutations during their life span is high. These mutations are called sporadic mutations and they are responsible for more than 90% of all cancer cases. It’s clear that those mutations are not inherited, but some environmental risk factors may contribute to having such mutations, such as cigarette smoking, radiation exposure, abnormal hormonal exposure, and certain types of diet. As we grow to adulthood, the risk of having accidental mutations is greater. Sporadic mutations will accumulate over time leading to accumulations of abnormal cells with uncontrolled growth and finally develop into a cancer.

When should you worry about cancer risk?

If your family has many reported cases of cancer, it’s most likely due to two reasons: either it’s an accidental finding as cancer is very common these days, or because of some shared risk factors, such as cigarette smoking or alcohol. In general, the risk of getting cancer due to inherited genes from family is low.

In medicine, an established term which describes those cases of cancer that run in families is known as familial cancer syndromes. There are certain red flags that may indicate the possibility of having a high risk of inherited cancer. The following are some of them:

  1. Cases of rare or very uncommon cancers in family such as kidney cancer.
  2. Early onset of cancer in the family, for example, a 20 year-old male with colon cancer.
  3. Two or more types of cancers in the same person, such as a woman with breast and ovarian cancers.
  4. Cancers that affect a pair of organs, for example, a man with kidney cancer in both kidneys.
  5. Two or more cases of childhood cancers in siblings, such as a brother with childhood sarcoma and a sister with childhood retinoblastoma.

Not all diagnosed cancer cases in a family are relevant!

Before relating any cancer cases in your family to your risk, you have to make certain of the following points:

  1. The number of relatives who are affected,
  2. Type of cancer that had been diagnosed,
  3. The age of the relative when diagnosed with cancer,
  4. Types of cancer that she/he had,
  5. Any possible risk factors that may be related to the type of cancer she/he had especially smoking.

It’s well-known that cancer in close relatives, especially parents and siblings, is more relevant than cancers in distant relatives and the type of cancer is important. More than two diagnosed cases of rare cancers are more worrisome than more than four diagnosed cases of common types of cancers. In addition, having multiple relatives with the same type of cancer is more relevant that having multiple relatives with different types of cancer. The age of the relative at the time of diagnosis is very crucial. For example, if you have a relative who is less than 30 years old who had colon cancer, it is highly suggestive of inherited cancer syndrome.

Finally, some cancers are closely related to certain risk factors, such as lung cancer vs. cigarette smoking. If you have more than two relatives who are smokers and they were diagnosed with lung cancers, it’s more likely that their cancer was due to smoking rather than inherited genes.