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 maintain 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 inactivated.
Most of people are born with healthy genes, but the chance of having mutations during their life span are high. Those 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 rick factors may
contribute in having such mutations such as cigarette smoking, radiation exposure, abnormal hormonal exposure, and certain types of diet. As we grow up, the
risk of having accidental mutations are higher. Those sporadic mutations will accumulate over time leading to accumulations of abnormal cells with
uncontrolled growth and finally development of cancer.
When should you worry about cancer risk?
If your family have 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 day, or
because of some shared risk factors such as cigarette smoking or alcohol. In general, risk of getting cancer due to inherited gene that is carried over families
In medicine, there is an established term which describes those cases of cancers that run in families known as familial cancer syndromes. There are certain
red flags that may indicate the possibility of having a high risk of inherited cancer. 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 family, for example, a 20 years old boy with colon cancer.
3- Two or more types of cancers in the same person such as a lady 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 degree 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, type of cancer is important
here. More than two diagnosed cases of rare cancers is 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 young and less than 30 years who had colon cancer, this is highly suggestive of inherited
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.
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Certain types of cancer can run in families via their genes. Cancer maybe inherited
through abnormal diseased genes which can run from a generation to the next one!
Despite this fact, not more than 5% to 10% of all cancer cases are inherited!
Basically, cancer is caused by abnormal genes on damaged DNA. DNA is the
instructions storage of the cell, it contains millions of genes; each of these genes
carries certain instructions for the cell to produce certain type of protein that has
its own function in the cell. In fact, our genes control 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 run from parents to children. They are in every single cell of a body as they are
inherited in the first place.
2- Acquired mutations or somatic mutations are those mutations which occurred accidentally during life. They are much more
common, and they are present in one cell only, not in all body cells as inherited mutations.
Carried genes in DNA are in special arrangement of strands; those strands known as chromosomes. We, as human beings, have 23
pairs of chromosomes in every single cell; one of those pair from mother and the others from 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 zygote. Zygote divides and creates fetus which later becomes an infant and then an adult. The one cell
Zygote formed from mother's egg, and sperm from father is the main source of each cell.
The acquired gene mutation also called somatic is not inherent in zygote or sperm. As the name suggest, it is acquired later. The
acquired gene mutation occurs in a certain cell, then it passes into another cell during the process of cell division. Since inherent gene
mutation is not present in the egg or sperm, hence it cannot pass that into next generations. Somatic gene mutation is more common
compared to inherited gene mutation. Vast majority of cancers develop as result of acquired gene mutations.