What we will cover in this article

What is Cancer?

How does cancer form?

Differences between Cancer Cells and Normal Cells

What Causes Cancer?

Environmental Causes of CancerTypes of Cancer

What is Cancer?

Cancer is a disease of the body. The body is made of a community cells, and each cell has a role to ensure that it functions smoothly. For example, the nerve cells must transmit neural signals, lung cells are involved in gaseous exchange, and intestinal cells must absorb nutrients from the digestive tract. Each cell in the body has a defined role, space and location.

Normally, cells do not cross their boundaries to enter into the spaces of other cells. Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. (National Cancer Institute, 2015) Over 100 types of cancers affect humans.  In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues. Cancer can start almost anywhere in the human body.

How does cancer form?

Cells divide by mitosis to form new cells when the body needs them. It is regulated by the cell cycle. When cells grow old or become damaged, they die, and are replaced by new cells. Sometimes cells become abnormal, and old or damaged cells continue to live when they should die. New cells are formed when they are not needed and this causes problems in the body. These new needless cells grow uncontrollably and may form outgrowths known as tumours. This will then push normal cells out of the way and use up all of the nutrients in the body to fuel their own uncontrolled growth. Tumours are classified as benign or malignant.

Benign tumours are largely not life threatening. Some benign tumours however, especially those that develop in the brain can be life threatening or even lead to death. The brain is encased in the cranium. The cranium has almost a fixed size, and continual expansion of benign tumours may damage the healthy brain. Malignant tumours on the other hand are always serious and will often lead to death if not detected and treated promptly. Malignant tumours can spread to other tissues through a process called metastasis.

A picture showing the proliferation of a cancerous cell.
This diagram illustrate how cancer is formed. Normal cells have similar shapes and size as shown in the first drawing labelled normal. As a person ages, their cells keep developing mutations. At a point, a normal cell develops enough mutations that it begins to grow slightly faster than the cells around it (the reddish cell in the center of the second drawing, labeled “single hyperproliferative cell”). Hyperproliferative means the cell grows faster than normal cells. When enough hyperproliferative cells accumulate, a small benign tumor called an adenoma develops (third drawing). The adenoma does not have the normal organization but it has not broken through the basement membrane. With time, the adenoma progresses into a carcinoma. The cells in the carcinoma break through the basement membrane and spreads to the spaces of other cells. Look at the fourth drawing, a tumor cell can be seen in the lower right-hand corner breaking into a small blood vessel (pink segmented circle). It will spread to other tissues through the bloodstream. This process is known as metastasis.

Differences between Cancer Cells and Normal Cells

  • Normal cells grow into specialised cells with specific functions, cancer cells do not specialised. Unlike normal cells, cancer cells continue to divide without stopping. They are less specialised than normal cells
  • Cancer cells no longer obey commands from proteins and genes that regulates cell multiplication and cell death. They ignore signals that instruct cells to stop dividing. They do not also listen to signals that activate programmed cell death, or apoptosis. This is the way the body gets rid of damaged, worn out or needless cells.
  • Cancer cells can direct blood vessels to supply tumours with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumours.
  • Cancer cells can hide from immune response. The immune response protects the body against pathogens and disease-causing agents. It also removes dangerous cells. It keeps the immune system from destroying cancer cells.

What Causes Cancer?

G pictorial representation of normal and cancerous cells

Cancer is a genetic disease meaning that it results from changes in the genes of an organism. This should not be taken as cancer is a hereditary disease. Hereditary diseases are transmitted from parents to offspring through genes. However, a person may have genes that makes them susceptible to cancer. The accumulation of mutations for a long period is the major cause of cancer. Not all genetic changes results in cancer; only changes in certain genes. These genes are categorized into three—proto-oncogenes, tumour suppressor genes, and DNA repair genes.

What are protooncogenes?

Proto-oncogenes are involved in the promotion of cell growth and multiplication. However, when these genes are altered in certain ways or become hyperactive, they be able to cause cancer. Cells that causes cancer are termed oncogenes.

What are Tumour Suppressor Genes?

Tumour suppressor genes are essential in the inhibition of cell growth and multiplication. If these genes lose their ability to inhibit cell growth and multiplication, cells may grow uncontrollably. And the chances of cancer is much higher.

What are DNA repair genes?

DNA repair genes repair DNA in the cell. Cells continually mutate and these genes help repair them. When these genes have mutations themselves, they may transfer it to the genes they repair thereby amplifying chances of getting cancer.

Do Viruses cause cancer

Oncoviruses refers to a group of viruses that has cancer causing abilities. This include hepatitis B and hepatitis C viruses (hepatocellular carcinoma), Kaposi’s sarcoma herpesvirus (Kaposi’s sarcoma and primary effusion lymphomas), human papillomavirus (cervical cancer), Epstein–Barr virus (B-cell lymphoproliferative disease and nasopharyngeal carcinoma),   and human T-cell leukemia virus-1 (T-cell leukemias). Bacteria can also pose a cancer risk, as seen in Helicobacter pylori-induced gastric carcinoma. Parasitic infections associated with cancer include Schistosoma haematobium (squamous cell carcinoma of the bladder) and the liver flukes, Opisthorchis viverrini and Clonorchis sinensis (cholangiocarcinoma).

Environmental Causes of Cancer

Genetic causes of are caused not only through mutation but by also environmental factors such as heat, radiation, chemicals, etc. These factors or agents that causes cancer are known as carginogens. Many non-melanoma skin cancers are due to ultraviolet radiation, mostly from sunlight. Sources of ionizing radiation include medical imaging and radon gas. Radiation exposure such as ultraviolet radiation and radioactive material is a risk factor for cancerPresented below is table of common carcinogens and the type(s) of cancer they are likely to cause.

CarcinogenOccupational ExposureCancer Risk
4-aminobiphenylChemical and dye workersBladder
ArsenicMining, pesticide workersLung, skin, and liver
AsbestosConstruction workersLung
AuramineDye workersBladder
BenzeneLeather, petroleum, rubber, and chemical workersLeukemia
BenzideneChemical, dye, and rubber workersBladder
Bis (chloromethyl) etherChemical workersLung
ChromiumMetal workers, electroplatersLung
Isopropyl alcoholManufacturing by strong acid processLung
Leather dustBoot and shoe manufacturing and repairNasal and bladder
Mustard gasMustard gas workersLung, larynx, and nasal
NaphthylamineChemical, dye, and rubber workersBladder
Nickel dustNickel refiningNasal and lung
RadonUnderground miningLung
Soots, tars, and oilsCoal, gas, and petroleum workersLung, skin, and bladder
Vinyl chlorideRubber workers, polyvinyl chloride manufacturingLiver
Wood dustsFurniture manufacturingNasal
Adapted from LSU Health Sciences Center

Types of Cancer


Carcinomas are formed from epithelial cells. Epithelial cells cover the inside and outside surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when viewed under a microscope. There various groups of carcinomas:


 This form of cancer affects glandular tissues; tissues that produce fluids or mucus. Example of tissues that gets adenocarcinoma include: breast, colon (large intestine), and prostate gland.

Basal cell carcinoma

This form of cancer begins in the lower or basal (base) part of the epidermal layer of the skin.

Squamous cell carcinoma

Squamous carcinomas are also called epidermoid carcinomas. These cells lie under the upper surface of the skin. They also form linings on tissues and organs like the stomach, intestines, lungs, bladder, and kidneys.

Transitional cell carcinoma

 This is a cancer of the transitional epithelium, or urothelium. Transitional epithelium also known as urothelium is common in the bladder, ureters, renal pelvis of the kidneys and a few other organs.


Sarcoma refers to cancer of the soft tissues of the body. This include tendons, muscle, fat, blood vessels, lymph vessels, nerves, etc. Sarcoma of the bone is termed osteosarcoma. Other types of sarcomas include liposarcoma, dermatofibrosarcoma protuberans, leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma,  etc. .



Leukemia is a cancer of the bone marrow. Red bone marrow help make blood cells. Leukemias do not form solid tumours. Large number of abnormal white blood cells enter the blood stream and impede the functions of normal blood cells. Normal blood cells are reduced in number and this in tend affect the levels of oxygen in the blood. It also inhibit blood clotting during bleeding and lower the person’s ability to 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).


Among the lymphocytes are T cells and B cells. These are white blood cells that helps the body fight diseases. Lymphoma results when abnormal lymphocytes accumulate at the lymph nodes and lymph vessels. It is categorized into Non-Hodgkin lymphoma and Hodgkin lymphoma.

Multiple Myeloma

Multiple myeloma also known as Kahler disease or plasma cell myeloma affects the immune system. It affects myeloma cells (plasma cells). These cells build up in the bone marrow and form tumour patches across the bones of the body.


Melanoma is cancer of the melanocytes. Melanocytes are specialized cells that produces the skin pigment melanin. Melanomas are commonly associated with the skin but they may affect other pigment containing tissues such as the eye.

Brain and Spinal Cord Tumours

These tumours associated with the central nervous system. Cancer of star shaped cells (astrocytes) in the brain is called astrocytic tumour. 


Other Types of Tumours

Germ Cell Tumours

This refers to tumours of the reproductive cells i.e. the sperm and the egg.

Neuroendocrine Tumours

This tumour affects tissues that produces and secretes hormones into the blood in response to a nervous signal. These tumours, which may make higher-than-normal amounts of hormones, can cause many different symptoms. Neuroendocrine tumours may be benign or malignant.

Carcinoid Tumours

Carcinoid tumours are slow growing and are found in the gut. Specifically the small intestine and the rectum. This tumours can metastasize to other parts of the body such as the live. They secrete the hormone serotonin or prostaglandins, causing carcinoid syndrome.

Many cancers are treatable especially when detected early. The importance of healthy life and diet cannot be over emphasised in preventing and managing any health problems. Scientists are still racing to find many unanswered questions on cancer. Hopefully these answers would help medics to better diagnose and cure cancer in the future.

Disclaimer: This is for educational purposes only. Health advise and care must be sought from accredited health professionals and institutions.

Further read:

What is cancer by the National Cancer Institute

Genetics of Cancer by LSU Health Science Center


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