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THE LINK BETWEEN CANCER AND GENETICS

  • Our bodies contain over 50 trillion tiny cells, and almost every one of them contains a complete set...

The link between Cancer and Genetics

Our bodies contain over 50 trillion tiny cells, and almost every one of them contains a complete set of instructions for making us who we are. These instructions are encoded in molecules called ‘DNA’. Long chains of DNA in our cells are organized into pieces called chromosomes. Humans have 23 pairs of chromosomes.

Genes are the set of instructions that help build, regulate and maintain our body functions. For example, building bones, enabling muscles to move, controlling digestion, and keeping the heart beating.

If chromosomes are a recipe book, genes are the single recipes in that book.

If we re-write and make many copies of that recipe book, there would certainly be a chance for error during replication. Gene mutations are those errors or “spelling mistakes” in the DNA that could either be inherited from a parent (thus present from birth and in each cell of the body) or spontaneous – those which occur during one’s life and are present only in certain cells, such as the lung or the stomach. Such spontaneous changes can be caused by environmental factors including ultraviolet radiation from the sun, but can alternatively occur if a mistake is made as DNA replicates when the cells reproduce in everyday life.

The cells in our bodies are replaced through an orderly process of cell growth and division. Healthy new cells take over as old ones die out. However, over time, mutations can “turn on” certain genes that control cell division, and “turn off” others that regulate cell growth. That changed cell gains the ability to keep dividing without control or order, producing more cells just like it and forming a tumor. These mutations are the cause for cancer (growth of abnormal cells that could lead to tumor formation).

Although some types of cancer run in families, most cancers are not clearly linked to the genes we inherit from our parents. Gene changes that start in a single cell during the course of a person’s life cause most cancers. These are called sporadic or acquired mutations.

This type of mutation is not present at birth, but is acquired later in life. It starts in one cell, and then is passed on to new cells that are the products of that cell. As this kind of mutation is not present in the sperm or the egg, it cannot be passed down to the next generation, and is considered an acquired mutation – which are more common than inherited mutations. In fact, most cancers are thought to be caused by acquired mutations.

Cancer is such a common disease that it is of no surprise that many families have at least a few members who suffer from it. Sometimes, certain types of cancer seem to run in some families, however only a small portion of all cancers are inherited.

Experts agree that it takes more than one mutation in a cell for cancer to occur. Thus when someone has inherited an abnormal copy of a gene, their cells already start out with one mutation. This makes it easier and quicker for a second mutation to occur for the cell to become cancerous. That is why cancers that are inherited tend to occur earlier in life than cancers of the same type that are not E.g. Breast cancer and colon cancer

Clearly some types of cancer are more common than others – up until recently, the two causative factors that were linked to cancer were hereditary and environment (including UV exposure; cigarette smoking; and obesity).

This makes perfect sense for conditions such as lung cancer, where the link to cigarette smoking is so strong and obvious. Whereas conditions such as breast cancer have clearer associations with inherited genetic mutations in the BRCA 1 and 2 genes. There are still many cancers however for which the links to either environment or inherited genetic mutations is unclear.

A new school of thought raises an intriguing possibility about another source of genetically determined cancer risk. In a recent article published in the Science Journal, the authors examined the distribution of stem cells within certain organs of the body, measured the number of divisions of these stem cells, and then plotted it against the lifetime risk of developing cancer in each of these organs.

Extremely interesting findings showed that organs in the body where stem cells divide many times are much more likely to develop cancer than those where the number of stem cell divisions are lesser. The authors suggested that stem cell DNA spelling mistakes were a possible cause of cancer in these organs because of the high number of cell replications.

This theory thus raises the question; “Are most cancers therefore a result of sheer “bad luck” of a healthy dividing cell making a random mistake while replicating its DNA?”

Early detection through regular and timely screening, and management via preliminary treatment and therapy has always been the professed weapon to combat cancer. With the new hypothesis of cancer occurring due to the result of “bad luck” during cell division and replication, this weapon becomes even more significant.

If there is no controllable factor to evade the risk of cancer, the only way to lessen the effect of the disease is through early detection and treatment.

Genetic counselors are certified healthcare professionals who can assess a person’s risk of developing an inherited cancer by studying their complete medical and family history. A genetic counselor will present the appropriate testing options to identify any familial mutation that may be present. Similarly, a counselor will discuss the various outcomes of testing and explore the impact that they could have on an individual and their family. Once the results are available, the counselor will interpret and explain them in detail and reassess the cancer risk based on the results. The patient will be presented with risk management options and specialist referrals if required.

To date, 12% of the population in the UAE suffer from cancer (Statistics from WHO in 2014).Breast cancer among women is the leading cause of death from cancer in the UAE, followed by colorectal cancers. As per the WHO, if no interventions are made, the rate of cancer cases could double by the year 2030 in the Eastern Mediterranean region (including the Middle East).

In order to reduce the morality from cancer, a number of factors need to be addressed such as access to regular and affordable screening for the general population, advanced research that could lead to a greater understanding of the disease in the region and thus better targeted treatments. There is also a need for improved data entry and reliable public registries to understand what we are facing, as well as access to accurate regional statistics.

 

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