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Cancer: Who, What, Where, When, Why, and How

 

Who

In the United States, about 39.6% of men and women will be diagnosed with cancer at some point in their lifetimes. African Americans and non-Hispanic whites are significantly more likely to deal with cancer than Hispanic Americans, American Indians, Alaska Natives, Asian Americans, or Pacific Islanders. Men are more likely than women to get it.

 

What
Basic genetics--what is a mutation?

Cancer is the second most common cause of death in the United States. 

It’s not a single disease, but a family of over 100 separate diseases in which the commonality is that cells divide without stopping and spread into surrounding tissues.
 

In cancer, cells survive after they would normally die due to damage, and they continue splitting into new cells unnecessarily. The extra cells are called tumors, which can spread to other parts of the body.

In many ways, cancer cells are unique. They don’t specialize in function like normal cells. They can ignore the chemical signals that lead to cell death. They can influence the surrounding environment—one way they do this is by causing blood vessels to form in order to sustain the tumor. They can hide from the immune system and hijack some of its cells to protect the tumor.

Cancer is a genetic disease, caused either by mutations that were inherited or by mutations that were caused by a person’s environment or lifestyle. Everyone’s cancer is genetically unique. There are even be different genetic changes between cells in the same tumor.

 

Where
Breast cancer cells

Cancer can begin almost anywhere in the body. The most common locations are in the breasts, lungs, prostate, colon or rectum, skin, and bladder.

When tumors spread into other parts of the body, it’s called metastatic cancer. When this happens the new tumor often has many of the same characteristics as the original, but it can have different genetic changes. This means cancer is often more difficult to treat once it has metastasized—those tumors may have slightly different properties. Metastatic tumors can severely damage bodily function and are the most common cause of cancer death.

 

When

Older people are more likely than younger people to get cancer. When young people, like children, have cancer it’s often a result of directly inheriting a genetic mutation that lead to their disease.

 

Why

It’s estimated that 5 to 10% of cancers worldwide are from directly inherited genetic mutations, with the remaining 90 to 95% being a result of mutations from a person’s environment or lifestyle.

Some of these factors include smoking, drinking, eating diets high in red meat or fried food, sun exposure and other radiation, pollution, infections, stress, obesity, and physical inactivity.

Smoking or tobacco use is linked to 25-30% of cancer cases. 30-35% is related to diet. 15-20% of cases are associated with infections, and up to 10% of cases have to do with radiation. These are the most common environmental/lifestyle factors in cancer worldwide.

It may seem strange that body weight and physical activity are linked to cancer, but it’s true. Excess body weight is associated with many types of cancer and is considered a factor in up to 14-20% of cancer deaths in the U.S. Weight and inactivity are thought to contribute to the risk of developing cancer because they have negative effects on the immune and endocrine systems.

As for infections, most of the time it’s viruses that can lead to cancer. The most well-known are HPV, which can lead to cervical cancer, or hepatitis B and C.

 

How

Every day, approximately 50-70 billion new cells are made in the human body, depending on factors like size and activity (like injuries). That’s about 579,000 to 810,000 every second. A new cell is made when an older one splits into two—this is called cell division. In the course of cell division, the DNA in a cell has to be copied, so the new cell also has DNA. Without any type of regulation, this process would yield mutations in about 1 in 10,000 genetic base pairs—those are the As, Cs, Ts, and Gs, in your DNA—or about 3,000 mutations per cell. If that sounds like a lot, that’s because it is. This level of mutation would be intolerable considering that each mutation has the potential to render an entire gene useless.

Gratefully, the human body has several processes to repair mutations, reducing that number to about 1 in a billion, which is about 3 per new cell.

At its heart, cancer is a failure to regulate this process. Because of that failure, one mutation leads to a cascade of mutations, and eventually to the uncontrolled cell division that we call a tumor.

Similar to the way in which a driver of a car takes that car to its destination and a passenger is just along for the ride, in cancer a driver mutation provides the driving force for tumor formation and spread while more than 99% of the mutations are just along for the ride. A given case of cancer usually has between 2 and 8 driver mutations, whose effect is cumulative. This is why a cocktail of different drugs is sometimes the best treatment for cancer; those driver mutations can work in completely different ways and each may need specific attention in order to stop the spread of cancer.

There are three main types of genes in which mutations drive cancer:

Henrietta Lacks and her immortal cancer cells
  1. Proto-oncogenes are involved in the cell division process. When altered, they can cause cancer and are then called oncogenes.
  2. Tumor suppressor genes are also involved in cell division: their role is to keep the process functioning at the correct rate. Mutations in them leads to fast, uncontrolled division and therefore creation of many new cells.
  3. DNA repair genes fix damaged DNA. When a mutation happens in a DNA repair gene, that prevents it from fixing mutations in other genes—including in proto-oncogenes and tumor suppressor genes.

Once cells are dividing uncontrollably and a tumor is forming, cancer cells can divide continuously as long as they have the proper amount of nutrients and space to grow.

All the changes to a normal cell that end in cancer and metastasis take time. In fact, there are years between the first mutation and the first symptom. For instance, pancreatic cancer begins 10 to 15 years before its first symptom is felt. As another example, when lung cancer is a result of smoking, it may not be symptomatic for two decades after the first mutation occurs.

 


Sources:

Alberts, Bruce. Essential cell biology. New York: Garland Science, 2014.

Anand, Preetha, Ajaikumar B. Kunnumakara, Chitra Sundaram, Kuzhuvelil B. Harikumar, Sheeja T. Tharakan, Oiki S. Lai, Bokyung Sung, and Bharat B. Aggarwal. "Cancer is a Preventable Disease that Requires Major Lifestyle Changes." Pharmaceutical Research 25, no. 9 (2008): 2097-116. Accessed March 24, 2017. doi:10.1007/s11095-008-9661-9.

"Fast Stats." Surveillance, Epidemiology, and End Results Program. September 12, 2016. Accessed March 16, 2017. https://seer.cancer.gov/faststats/.

"Incidence & Mortality by Race/Ethnicity, CSR 1975-2013." Surveillance, Epidemiology, and End Results Program. Accessed March 14, 2017. https://seer.cancer.gov/csr/1975_2013/results_merged/topic_race_ethnicity.pdf.

Kushi, Lawrence H., Colleen Doyle, Marji Mccullough, Cheryl L. Rock, Wendy Demark-Wahnefried, Elisa V. Bandera, Susan Gapstur, Alpa V. Patel, Kimberly Andrews, and Ted Gansler. "American Cancer Society guidelines on nutrition and physical activity for cancer prevention." CA: A Cancer Journal for Clinicians 62, no. 1 (January 11, 2012): 30-67. doi:10.3322/caac.20140.

"Leading Causes of Death." Centers for Disease Control and Prevention. October 07, 2016. Accessed March 24, 2017. https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm.

Lewis, Ricki. Human Genetics: concepts and applications. New York: Mc Graw Hill, 2015.

"What Is Cancer?" American Cancer Society. December 8, 2015. Accessed March 14, 2017. https://www.cancer.org/cancer/cancer-basics/what-is-cancer.html.

"What Is Cancer?" National Cancer Institute. February 9, 2015. Accessed March 14, 2017. https://www.cancer.gov/about-cancer/understanding/what-is-cancer.

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