Unveiling the Genetic Landscape of Cancer

“There are two ways to be fools. One is to believe what isn’t true; or the other is to refuse to believe what is true.” –(Soren Kierkegaard)

cancer cell.jpgWhat would you do if you found out that cancer could be lurking in your genes? More people are getting news like that these days that more kinds of cancer are being linked to specific genes and genetic tests let doctors screen your individual genome for signs of susceptibility to the disease. But what if one of those tests comes back positive? Does that mean you are going to have cancer? Is there anything you can do? Is your DNA your destiny?

Consider Angelina Jolie, where she announced that she had a double mastectomy because genetics tests have revealed that she carried a mutation and one of her genes predisposed her to breast cancer.

 angelina-jolie-updo-highlights-sophisticated-brunette“In 2013, actress Angelina Jolie announced that she had undergone a preventive double mastectomy because she was a BRCA1 gene mutation carrier, which puts her at very high risk for breast and ovarian cancer. Jolie also had a family history of these cancers. Soon after, TIME wrote a cover story–“The Angelina Effect”–looking at what impact her decision could have on women who carry the dangerous BRCA1 and BRCA2 genes and therefore may be at risk for breast and ovarian cancers. Now, a new study being presented at the 2014 Breast Cancer Symposium shows that the Angelina effect is indeed real.” – TIME

Thousands of women in the United States make the same decision every year. And it makes sense in a lot of ways! A study at the University of Texas in 2009, state that 70% of women who tested positive for genetic mutations related to breast cancer thought that preventive mastectomy was the most effective way to reduce the risk. What’s interesting is that almost all of these women said that their decision was motivated and not necessarily wanting to be healthy or to live longer, but simply to rid themselves of the fear that they have felt since they got their test results. But look at the bigger picture here shows that being genetically at risk is by no means of death sentence and there is a whole spectrum of options for treatment. The mutations mentioned can occur on genes that everyone has, women and men, called BRCA1 and BRCA2.

In 1990s, the biotech company found certain mutations in these genes predispose their carriers to breast and ovarian cancer. The company actually use the genes and develop tests to identify the dangerous mutations. According to the National Cancer Institute, about 12% of women will develop breast cancer some time during their lives. But for women who have inherited a harmful mutation in one of those genes, the risk is about 60%, five times higher! However, the first thing we should keep in mind that these mutations are really rare, only 0.1-0.2% of the general population either carry the BRCA1 cancer-cellor BRCA2 cancer. And even the odds of developing cancer is greater if you have one of the, it is an increased risk not a diagnosis of disease. After all 40-80% of women who are genetically at risk do not end up getting either the breast or ovarian cancer. Maybe more importantly, genetic mutations are by no means the only cause of breast cancer. In fact, BRCA mutations account for 5-10% of breast cancer cases. Other causes vary widely from behavioral factors such as smoking to epigenetics, the role your environment plays how your genes are expressed. And for those who have the mutated BRCA genes, mastectomies aren’t the only treatment. Some women chose regular testing such as frequent mammograms, breast MRIs and clinical breast exams to look out for symptoms. And since breast cancers are fuelled by the hormone estrogen, scientists are also looking at estrogen-blocking drugs, as a way of preventing the disease. As depressing and terrifying as it may be, defined that could be predisposed to an incurable disease, there are options and therefore hope. And you have options because unlike the generations before, today we can hear what our genes are telling us and seek out treatment before we even have the disease.

The genetics of cancer refers to the inherited cancer traits passed from one generation to the next. Scientists do genetic testing to study if the genes of a particular patient have abnormalities and how these abnormalities affect their health and measure their risk to a certain disease. Just like Angelina Jolie, the BRCA1 gene she acquired is linked to a higher risk of breast cancer. Thus, if a person inherits an altered form of the BRCA1, he or she will have a higher risk of developing breast cancer. While genetics talks about molecular composition, cancer genomics involves decoding the DNA structure of tumor cells. This time, scientists do genomic testing to reveal characteristics which drive tumors where to spread and how to grow rapidly.

Many scientists have predicted the statistics on how cancer can be so diverse. So is it true that almost 50 percent of the people alive today will face cancer? Is it true that one in four males alive today will die from cancer? And one in five females will die from cancer? These statistics give enough reason for many good people to search out the answers. But first, we should all know how cancer is developed.

So the cells in the body are normally imbalance, they will see signals from their surroundings and from other cells telling them how to behave. The signals bind to receptors, the receptors trigger proteins in the cell to control cell proliferation. Inside the cell, some proteins tell the cell to calm down or multiply. Thus, these processes can help you repair injuries or fight infections. But, when bad things go badly, cancer develops.

dna-repair

The blueprint for our cells is the DNA, made of billions of nucleotides. When DNA is replicated, mistakes are made, some nucleotide becomes another nucleotide and the transcribed protein changes. Usually these changes are harmless, very rarely they can even be good and help a species evolve, but it can also cause great harm! A mutation in an oncogene, a gene that in certain circumstances can transform a cell into a tumor cell, can strengthen the damaged DNA and make it active without the usual pathway, shifting the balance of the cell to the oncogenes. To the same fact, a tumor suppressor can be broken by a mutation. Translocations in the genome can occur, which can make an oncogene multiply further. All of these changes will allow a group of cells to grow without control, creating a tumor hat invades and overruns the rest of the body.

The mutations created in a cancer cell genome have built up over time in a life of a cancer patient. Some mutations can be acquired from ancestors with cancer if the cancer cell is biologically normal, showing no characteristics of a phenotypic cancer cell. There are still less studies about the normal human cells’ somatic mutation rates which gives us very small understanding about it. However, mutation rate of several structural forms of somatic mutation differ, thus there are differences among other cell types too. In some instances, if a single nucleotide changes or a small nucleotide in the DNA is inserted or deleted, other classes of phenotypic mutation may exist, forming abnormalities in the chromosome number which increases the somatic mutation rate. The advantage increased rate is that it increases the DNA diversity on which selection can occur with respect to its relationship on the development of cancer.

The modern treatment of cancer focuses on targeting these proteins, the proteins that controls cell growth. As we all know, the cells in the body grow and divide as part of the normal cell cycle, where the cell’s nucleus controls this process. Inside each nucleus, genetic material, DNA, contains instructions for directing the processes. As discussed earlier, sometimes the DNA is damaged. Normally the DNA responds by repairing itself or instructing the cell to die. In cancer however, the part of the cell’s DNA that direct the cell division become damaged. When these sections are damaged, the DNA is unable to repair itself or cause the cell to die. Instead, the unrepaired DNA causes the cell to grow and divide uncontrollably by more damaged cells called cancer cells. A tumor forms as the cancer cells multiply and displace the normal cells. As the tumor enlarges it develops its own blood supply. Since cancer cells do not stick together, as well as normal cells, they may break away and enter a nearby blood vessel. Cancer cells in blood vessels may travel to other areas of the body and form additional tumors, which is called metastasis. Other tumors may grow in other areas such as the lungs, liver and bones. Another way cancer can spread into your body is through your lymphatic system. Cancer cells may enter lymph vessels near the tumor, then travel to small glands called lymph nodes. If the cells pass through the nodes, they may continue to the lymphatic system and form additional tumors.

So if you have cancer, your doctor might recommend targeted cancer cell therapy. Targeted cancer therapy attacks features common to cancer cells, while limiting damage to your normal cells. There are two types of targeted therapy. One type includes small molecule drugs that work inside your cancer cells. The other type includes drugs called monoclonal antibodies that work on the outside of your cancer cells. These therapies work in one of four ways. Some block signals that cancer cells use to make new cancer cells. Others deliver toxic substances that kill or damage cancer cells. Some therapies stimulate cells in your immune system to destroy cancer cells. Others block the new blood vessels around the cancer cells which starves the cell of the nutrients they need to grow. Depending on the advice of the doctor, the patient may receive oral medication, injection or an intravenous infusion.

Nowadays, we sequence the genome of the cancer to try to find what’s driving it and how we can treat it. Some people have mutation in cancer genes from birth from their family. The BRCA gene in breast cancer is the most famous example. BRCA is a tumor suppressor that repairs damage to DNA. If it doesn’t work quite right from a mutation, a person will more likely to get cancer. So we sequence these genes in people with cancer and their families to try to determine their risk. This is the answer on how scientists made their predictions on cancer diversity.  Some mutations can tell the person’s risk for cancer but sometimes we find a new rare and unique mutation never seen before. A variant of an unknown significance and in some case, it’s anyone’s guess, is stressful for the patient. But the body can be unpredictable, and even if 90% of people with a certain mutation get cancer, 10% still don’t.

References:

http://www.nature.com/ng/journal/v33/n3s/full/ng1107.html

http://www.nature.com/articles/nature07943

https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet

https://www.eurekalert.org/pub_releases/2012-12/jaaj-ser121312.php

https://www.eurekalert.org/pub_releases/2009-03/uotm-wwb030509.php

https://www.cancer.gov/types/breast/risk-reducing-surgery-fact-sheet

https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet

http://www.cancercenter.com/discussions/blog/whats-in-a-name-genetics-vs-genomics/

https://www.niehs.nih.gov/health/assets/docs_a_e/environmental_factors_and_breast_cancer_risk_508.pdf

Author: Jodelyn M. Brazas

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