Cancer: The Silent Predator
Photo by National Cancer Institute on Unsplash
Cancer other name tumor/neoplasm is dubbed as the “silent predator or killer” because its vague symptoms make early detection difficult. Cancer is a disease of the body's cells in which some of the cells grow uncontrollably and spread to other parts of the body through the blood and lymph systems. Cancer can start almost anywhere in the human body, which is made up of trillions of cells. It can press on nearby nerves and cause pain and loss of function of that part of the body.
A tumor can be benign or malignant. A malignant tumor has irregular borders, grows faster than a benign tumor and can also spread to other parts of the body (a process called metastasis) in contrast to benign tumor. Benign tumors can sometimes be quite large, however, some can cause serious symptoms or be life threatening, such as benign tumors in the brain. [1]
There is also the starvation aspect of cancers suppressing the appetite and tumor cells taking up all the nutrients for themselves at the expense of body’s normal cells. This may or may not be fatal in and of itself, but it certainly doesn't help deal with the rest of complications cancers bring. Possible signs and symptoms include a lump, abnormal bleeding, prolonged cough, unexplained weight loss, and a change in bowel movements. While these symptoms may indicate cancer, they can also have other according in relation with the causes.[2]
Difference Between A Normal Cell And A Cancerous Cell
Cancer cells differ from normal cells in many ways. Normally, cells follow instructions provided by genes. Genes set down rules for cells to follow, such as when to start and stop growing. Cancerous cells ignore the rules that normal cells follow:[2]
Major Causes Of Cancer
There are a number of chemical, physical and biological agents that have been shown to trigger the mistakes in the cell blueprint that cause cancer. These are called carcinogens; and include following: [3]
· Physical: ultraviolet and ionizing radiation;
· Chemical: asbestos, components of tobacco smoke, alcohol, aflatoxin (a food contaminant), and arsenic (a drinking water contaminant);
· Biological: infections from certain viruses, bacteria, or parasites.
Cancer may be caused by changes in genes that control the way the cells function, especially how they grow and divide. Genes are the basic physical units of inheritance. They are arranged in long strands of tightly packed DNA called chromosomes which determine the structure, function and behaviour of a cell. A gene can mutate. Mutated genes don't work properly because the instructions in their DNA get mixed up. This can cause cells to grow out of control, which can lead to cancer.
A gene mutation can instruct a healthy cell to:
· Allow Rapid Growth and divide more rapidly. This creates many new cells that all have that same mutation.
· Fail To Stop Uncontrolled Cell Growth. A mutation in a tumor suppressor gene allows cancer cells to continue growing and accumulating.
· Make Mistakes When Repairing DNA Errors. DNA repair genes look for errors in a cell's DNA and make corrections. A mutation in a DNA repair gene may mean that other errors aren't corrected, leading cells to become cancerous.
Gene mutations occur frequently during normal cell growth. However, cells contain a mechanism that recognizes when a mistake occurs and repairs the mistake. Gene mutations can occur in following ways:
· People Are Born With. inherited from parents.
· Gene Mutations That Occur After Birth. Most gene mutations occur after one is born and aren't inherited. A number of forces can cause gene mutations, such as smoking, radiation, viruses, cancer-causing chemicals (carcinogens), obesity, hormones, chronic inflammation and a lack of exercise.[3]
Tobacco use is the cause of about 22% of cancer deaths. Another 10% are due to obesity, poor diet, lack of physical activity or excessive alcohol consumption. Other factors include certain infections, exposure to ionizing radiation, and environmental pollutants. Infection with specific viruses, bacteria and parasites is an environmental factor causing approximately 16-18% of cancers worldwide. These infectious agents include Helicobacter pylori, hepatitis B, hepatitis C, human papillomavirus infection, Epstein–Barr virus, Human T-lymphotropic virus 1, Kaposi's sarcoma-associated herpesvirus and Merkel cell polyomavirus. Human immunodeficiency virus (HIV) does not directly cause cancer but it causes immune deficiency that can magnify the risk due to other infections, sometimes up to several thousand fold (in the case of Kaposi's sarcoma). Importantly, vaccination against hepatitis B and human papillomavirus have been shown to nearly eliminate risk of cancers caused by these viruses in persons successfully vaccinated prior to infection.
These environmental factors act, at least partly, by changing the genes of a cell. Typically, many genetic changes are required before cancer develops. Approximately 5–10% of cancers are due to inherited genetic defects.[4] [5] [6]
Photo by National Cancer Institute on Unsplash
Cancer In Males Vs Females
The analysis suggests that biological differences between the two sexes account for the imbalance, rather than behavioral or lifestyle factors, such as smoking and alcohol use, body mass index, height, physical activity, diet, medications, and medical history. According to the National Cancer Institute (NCI) men are more likely to develop cancer than women. Men have a one in two chance of being diagnosed with cancer during their lifetimes; for women, the chance is one in three.[7]
The most common cancers for men and women are listed in order below:
The ‘Protective Advantage’ Of The X Chromosome
According to one research the women may have a protective advantage. It’s something intrinsic in the male and female system. The X chromosome contains several tumor suppressor genes and females may have higher expression levels because they have two Xs instead of the one that males have. There are of course also differences in hormones like estrogen and testosterone, activity of the immune system in men and women, and other factors that could influence these differences.
Men with certain types of leukemia often possess mutations on genes located on the X chromosome. These mutations damage tumor-suppressor genes, which normally halt the rampant cell division that triggers cancer. Whereas females, who have two X chromosomes, would be less prone to these cancers because they have two copies of each tumor suppressor gene. In contrast, men have an X and a Y chromosome—or just one copy of the protective genes, which could be “taken out” by mutation.[7]
Types of Cancer
There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer and brain cancer. Cancers also may be described by the type of cell that form them, such as an epithelial cell or a squamous cell. Some categories of cancers begin in specific types of cells: [8]
· Carcinoma- Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. Carcinomas that begin in different epithelial cell types have specific names:
· Adenocarcinoma forms in epithelial cells that produce fluids or mucus. Tissues with this type of epithelial cell are sometimes called glandular tissues. Examples are breast, colon, and prostate cancers.
· Basal cell carcinoma begins in the lower or basal (base) layer of the epidermis, which is outer layer of skin.
· Squamous cell carcinoma forms in squamous cells, which are epithelial cells that lie just beneath the outer surface of the skin. Squamous cells also line many other organs, including the stomach, intestines, lungs, bladder, and kidneys.
· Transitional cell carcinoma forms in a type of epithelial tissue called transitional epithelium, or urothelium found in the linings of the bladder, ureter, and part of the kidney (renal pelvis), and a few other organs.
· Sarcoma- form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).
· Leukemia- Cancers that begin in the blood-forming tissue of the bone marrow are called leukemias. Large numbers of abnormal white blood cells (leukemia cells and leukemic blast cells) build up in the blood and bone marrow, crowding out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to its tissues, control bleeding, or fight infections. There are four common types of leukemia, which are grouped based on how quickly the disease gets worse (acute or chronic) and on the type of blood cell the cancer starts in (lymphoblastic or myeloid). Acute forms of leukemia grow quickly and chronic forms grow more slowly.
· Lymphoma- begins in lymphocytes (T cells or B cells). These are disease-fighting white blood cells that are part of the immune system. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body. There are two main types of lymphoma:
· Hodgkin lymphoma – These cells usually form from B cells.
· Non-Hodgkin lymphoma – This is a large group of cancers that start in lymphocytes. The cancers can grow from B cells or T cells.
· Multiple Myeloma- begins in plasma cells, another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumors in bones.
· Melanoma- begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color). Most melanomas form on the skin, but melanomas can also form in other pigmented tissues, such as the eye.
· Brain and Spinal Cord Tumors- There are different types of brain and spinal cord tumors and are named on the type of cell in which they are formed. For example, an astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy.
Other Types of Tumors
· Germ Cell Tumors- a type of tumor that begins in the cells that give rise to sperm or eggs.
· Neuroendocrine Tumors- form from cells that release hormones into the blood in response to a signal from the nervous system.
· Carcinoid Tumors- Carcinoid tumors are a type of neuroendocrine tumor usually found in the gastrointestinal system (most often in the rectum and small intestine).
The Cancer Rates Differ Between Developed And Developing Countries
There are more than 100 different types of cancer, but following five most diagnosed cancers in 2023 accounted for 60% of all total diagnosed including: prostate, followed by breast, melanoma, colorectal or bowel cancer, and lung cancer.
Overall, cancer incidence is higher in more developed countries, but rates of cancer are rising in many lower income countries. Generally, cancer rates are highest in countries whose populations have the highest life expectancy, education level, and standard of living. But for some cancer types, such as cervical cancer, the reverse is true, and the incidence rate is highest in countries in which the population ranks low on these measures.
According to one estimate a total of 19,976,499 cases of cancer were diagnosed in 2023. There were an estimated 9,296,171 cases of cancer per 100,000 people in areas with very high human development, compared with 812,211 in areas with low human development. There were an estimated 96 deaths from cancer per 100,000 people in areas with very high human development, compared with 77.3 in areas with low human development. The age-standardised rate for all cancers for men and women combined was 196.9 per 100,000. The rate was higher for men (212.6 per 100,000) than women (186.3 per 100,000).[9]
Although it may be tempting to anthropomorphize cancer and attribute human-like attributes to it, the reality is that cancer is driven purely by genetic mutations and an insatiable desire to multiply. It lacks the capacity for introspection or understanding the consequences of its actions. The cancer's inability to recognize the consequences of killing the host stems from its lack of consciousness, its selfish nature, and its disruption of communication within the body. By delving deeper into the mechanisms of cancer growth and studying its behavior, scientists hope to find new ways to combat this devastating disease.
References
1. "Defining Cancer". National Cancer Institute. 17 September 2007
2. "Cancer – Signs and symptoms". NHS Choices. Archived from the original on 8 June 2014. Retrieved 10 June 2014.
3. Parkin DM, Boyd L, Walker LC (December 2011). "16. The fraction of cancer attributable to lifestyle and environmental factors in the UK in 2010". British Journal of Cancer. 105 (Suppl 2): S77–81. doi:10.1038/bjc.2011.489.
4. "Heredity and Cancer". American Cancer Society. Archived from the original on 2 August 2013. Retrieved 22 July 2013.
5. "How is cancer diagnosed?". American Cancer Society. 29 January 2013. Archived from the original on 14 July 2014. Retrieved 10 June 2014.
6. "Obesity and Cancer Risk". National Cancer Institute. 3 January 2012. Archived from the original on 4 July 2015. Retrieved 4 July 2015.
7. "SEER Stat Fact Sheets: All Cancer Sites". National Cancer Institute. Archived from the original on 26 September 2010
8. Siegel RL, Miller KD, Wagle NS, Jemal A (January 2023). "Cancer statistics, 2023". CA. 73 (1): 17–48. doi:10.3322/caac.21763
9. Jemal A, Bray F, Center MM, Ferlay J, Ward E, Forman D "Global cancer statistics". CA. 61 (2): 69–90. doi:10.3322/caac.20107