Cancer is one of the most dreaded diseases of our time and in some case akin to receiving a death sentence. The news that you or a loved one have been diagnosed with cancer fill us with shock and apprehension. For many of us cancer is an unknown process hidden somewhere in the body, with the accompanying fear of the unknown. Gaining some insight into the nature of the disease can help to better deal with this news.
What is cancer?
Cancer refers to any malignant growth or tumor in the body, caused by abnormal and uncontrolled cell growth in some area. Cells are constantly renewing themselves, but when they get damaged in some way, the normal regular division of cells – with new cells forming and old ones dying off – goes haywire and cells in the affected area continue to divide and grow uncontrollably, and can invade surrounding tissue or spread to other areas in the body.
Normal cells:
The human body is made up of an estimated 30 trillion cells of many different types, such as cells of the skin, internal organs, muscle tissue, bones, and the brain, that all look different and have different functions.
Human cells grow into maturity to carry out their functions in the body, with the ability to divide to form new cells when needed to replace damaged or aging cells. The old or damaged cells undergo a process of programmed cell death or apoptosis, being replaced by new cells. A normal cell has a life cycle of growth, maturity, division, and death (apoptosis).
On average cells are replaced every 7 – 10 years, but the cells in different organs have a huge variability in lifespan. This ranges from neutrophils (make up 50-70% of white blood cells) that might last for 4 hours or less; sperm cells have a lifespan of only 3 days, while brain cells in the cerebral cortex, like the cells in the middle of the lens of the eye, last a lifetime. Cells that have died off on the surface of the body or in the lining of the gut are sloughed off and discarded, while those inside our bodies gets scavenged by a type of white blood cell called phagocytes that ingest the dead cells.
At the center of each individual cell is the nucleus, which contains the genetic material (with operating instructions) that determines the structure and function of that cell. The nucleus contains chromatin that is composed of DNA (deoxyribonucleic acid), which contains the codes for cellular function, cellular differentiation (cells becoming more specialized), and replication (DNA making a copy of itself during cell division).
The nucleus is the command/control center of the cell and sends instructions to the cell to grow, mature, divide, or die. The DNA in the nucleus is the cell’s hereditary material and nearly every cell in the body has the same DNA. DNA has the unique ability to replicate, meaning it can make exact copies of itself, which is crucial when cells divide, to ensure that each new cell has an exact copy of the DNA in the old cell. Billions of new cells are produced daily, which raises the question of why we age? Over time the DNA in cells become progressively unreliable and damaged, resulting in aging.
Cancer cells:
Cancer is caused by changes to the DNA in cells. Genetic changes that result in cancer can be inherited, or result from certain environmental exposures, or from errors that occur when cells divide. Normal cells obey the instructions contained in the DNA, but cancer cells are rebels! They refuse to obey these instructions and continue to grow and divide uncontrollably and avoid programmed cell death by not dying off when they should. This out-of-control growth result in the cancerous cells piling up and forming tumors, which can spread into surrounding tissue, or break away to travel to other areas in the body.
There are tumor suppressor genes in normal cells which prevent cancer, by slowing or even stopping cell growth, but DNA changes can inactivate the tumor suppressor genes, resulting in uncontrollable cell growth.
Normal cells can repair themselves if their DNA become damaged, but in cancer cells the molecules that decide whether a cell should repair itself, become faulty.
Cancer cells are not only rebels, but also conmen, as they can prompt the normal cells around them to grow new blood vessels to supply the tumors with nutrients.
The immune system’s cells normally detect and attack cancer cells, but these conmen can blindside the immune system by inhibiting the ability of the immune system to differentiate cancer cells from normal cells, preventing the immune system from removing damaged or abnormal cells from the body.
Cancer can start almost anywhere in the body or break away from the original tumor and travel via the bloodstream or the lymph system to other locations in the body, where they exit these carrier vessels to form new tumors. This process is called metastasis.
Benign cells are noncancerous, as they can overproduce and form tumors, but do not invade other tissue. They can become a problem if the size of the tumor affects an organ, for example a benign brain tumor.
Malignant cells are cancerous, with the ability to invade surrounding tissue and may spread throughout the body. Any cells left behind when a malignant tumor is removed can result in new cancerous growth.
Cancers of the blood generally do not form solid tumors, but they can cause abnormal blood cells to build up in the bloodstream.
Categories of cancer
There are more than 100 types of cancer, but they can broadly be classified based on the type of tissue in which the cancer originates (histological type) or the location where the cancer originated. The most common sites in which cancer develops are the skin, lungs, female breasts, prostate, uterus, as well as the colon and rectum.
The major categories, based on their histological characteristics, are
- Carcinoma – this is the most common form of cancer. Adenocarcinoma forms in cells of organs or glands that produce fluids, such as the breast, colon, and prostate. Basal cell carcinoma forms in the outer layer of skin. Squamous cell carcinoma forms in cells that lie beneath the outer surface of the skin, as well as in the lining of other organs such as the stomach, intestines, lungs, bladder, and kidneys. Transitional cell carcinoma occurs in the cells of tissue that can get bigger and smaller, such as the linings of the bladder, the ureters, and the renal pelvis part of the kidneys.
- Sarcoma – forms in supportive and connective tissues such as bone and tendons, ligaments, cartilage, muscle, fat, blood vessels, and lymph vessels.
- Leukemia – these “blood” cancers begin in the blood-forming tissue of the bone marrow and do not form solid tumors. Large numbers of abnormal white blood cells build up in the bone marrow and blood and cause the crowding out of normal blood cells. The reduction in the number of normal blood cells makes it harder to transport oxygen to the tissues in the body, and to control bleeding or fight infections. Leukemia also affects red blood cells and can cause fatigue due to anemia or cause poor blood clotting.
- Lymphoma – this is a cancer that starts in the disease-fighting white blood cells that form part of the immune system and builds up in lymph nodes and lymph vessels. It may also develop in other organs in the body connected to the lymphatic system – a network of lymph vessels and organs such as the lymph nodes, spleen, tonsils, and thymus gland.
- Myeloma – this cancer begins in plasma cells (another type of immune cell) that builds up in the bone marrow and form tumors in bones.
- Melanoma – this cancer begins in cells that make the pigment (melanin) that gives colour to skin. Melanoma usually forms on the skin, but it can also form in other pigmented tissue such as the eyes.
- Brain and spinal cord tumors – masses of abnormal cells that have grown out of control in the brain and spinal cord are referred to as tumors, rather than cancer, as their growth can press on and destroy surrounding brain tissue. Most tumors result from out of control growth among cells that support neurons, although the brain and spinal cord have many kinds of tissues and cells, which can develop into different types of tumors.
How to lower the risk of developing cancer
Although genetics can play a role in developing cancer, an inherited predisposition for cancer only plays a role in 2-3% of cases. It is well accepted in medical circles that lifestyle choices play a major role in increasing the risk of developing cancer, and research shows that up to 50% of cancer cases and deaths are preventable.
Harvard Medical School, the Mayo Clinic and other institutions involved with research and treatment of cancer, indicate several lifestyle changes that can lower the risk of developing cancer:
- Smoking – avoid the use of tobacco in all its forms, as smoking has been linked to many types of cancer, such as cancer of the mouth, throat, larynx, lung, pancreas, kidney, bladder, and cervix.
- Alcohol – drink alcohol in moderation (one drink per day), as the risk of various types of cancer, such as cancers of the liver, kidney, breast, colon, and lung have been linked to excessive intake and long duration in the use of alcohol. When excessive daily use of alcohol is combined with smoking 20 cigarettes per day, the risk of developing throat cancer is increased 48-fold.
- Eat properly – reducing the consumption of saturated fat, processed meat, red meat, and increasing the consumption of fruit, vegetables, and other plant sources such as legumes and whole grains can help to reduce the risk of various cancers.
- Exercise – regular daily exercise has been linked to a reduced risk of colon and breast cancer.
- Stay lean – obesity increases the risk of various types of cancer, while maintaining a healthy weight has been linked to a reduced risk of breast, prostate, lung, colon, and kidney cancer.
- Avoid unnecessary exposure to radiation – radiation from X-rays and other medical imaging studies are risk factors for cancer, while ultraviolet radiation from sunlight increases the risk of melanomas and other forms of skin cancer. Electromagnetic radiation from cell phones, microwaves or high-voltage power lines do not cause cancer, says Harvard.
- Toxins – exposure to environmental and industrial toxins have been linked to a higher risk of cancer, for example asbestos, benzene, vinyl chloride, arsenic, and beryllium are known carcinogens.
- Infections – certain infections, linked to sexually transmitted diseases or the sharing of hypodermic needles, can contribute to cancer, such as hepatitis viruses (linked to liver cancer), HIV, and the human papillomavirus (linked to cervical and other genital cancers).
Conclusion
We do all have cancer cells in our bodies. It is difficult to determine the exact reason why someone develops cancer, as a combination of factors may contribute to the first chance mutation (damaged DNA) in a cell, from where it is passed on to every cell it produces.
While our bodies constantly produce new cells, some may be produced with damaged DNA, but that does not mean all of them have the potential to become cancerous. Most cells with damaged DNA either repair themselves or die off through normal programmed cell death. However, sometimes such damaged cells are exposed to many more promotors (for example, smoking) over months and years, that eventually result in this damaged cell undergoing further DNA genetic damage (mutations) and this cell then loses control of normal growth regulation and becomes cancerous.
Sources:
Cancer cells. Published online and last reviewed 1 July 2020. Cancer Research UK. (www.cancerresearchuk.org)
Sugar and cancer – what you need to know. Published online and updated 11 July 2019. Cancer Research UK. (www.cancerresearchuk.org)
What is cancer? Published online and updated 9 February 2015. National Cancer Institute. National Institutes of Health. USA. (www.cancer.gov)
Does everyone have cancer cells? Published 18 June 2020. Healthline. (www.healthline.com)
How many cells are in the human body? Published online and updated 18 July 2018. Healthline. (www.healthline.com)
The nucleus and DNA replication. Published online. Oregon State University. USA. (www.open.oregonstate.education)
Cancer prevention: 7 tips to reduce your risk. Published online 28 November 2018. Mayo Clinic. USA. (www.mayoclinic.org)
Seven steps to prevent cancer. Published online. Prevent Cancer Foundation. USA. (www.preventcancer.org)
The 10 commandments of cancer prevention. Published online and updated 1 October 2019. Harvard Men’s Health Watch. Harvard Medical School. (www.health.harvard.edu)
HEALTH INSIGHT
October 2020