What is cancer?


The human body is compromised of millions and millions of cells. These cells grow and divide continuously so that new cells can take the place of cells that die when they become too old or too damaged; some, like those lining the gut or in the bone marrow, divide more rapidly than others. Cancer, which has been known to mankind since ancient times, occurs when some abnormal cells start to divide out of control. These cells then form what is called a mass, lump, or tumour. [1,2,3]


Human mummies from ancient Egypt provide the earliest evidence of cancer in the form of fossilised bone tumours. The Edwin Smith Papyrus, also from Egypt and dating back to about 3000 BC, contains a description of the disease, even though the word cancer was not used per se. Hippocrates (460 – 370 BC), a Greek physician known as the “Father of Medicine”, first named the disease after a crab due to the finger-like projections from cancerous growths that brought to mind the shape of a crab. He used to terms carcinos and carcinoma to describe non-ulcer forming and ulcer-forming tumours. [1]

Celsus, a Roman physician who lived from 28 to 50 BC, translated the Greek terminology to the Latin word for crab, i.e., cancer. Another Roman physician by the name of Galen (130 – 200 AD) used the term oncos (Greek for swelling) to describe tumours. Today the term oncology, of which oncos is the root, denotes the study of cancer. [1]

How cancer begins

Cell division is usually a tightly regulated process with only an exceedingly small margin of error. However, cancerous cells are able to escape from this orderly process and can multiply uncontrollably. These aberrant cells may form a mass or lump – this is known as a tumour. [2,3]

We differentiate between benign and malignant tumours. A benign, or non-malignant tumour, will grow and become larger where it originated, but will not spread to other organs. However, such tumours may be locally destructive and cause damage to surrounding tissues through pressure and displacement effects. Malignant tumours, on the other hand, are invasive and spread to other organs or parts of the body. [2,3]

Not all types of cancer form a tumour. Examples of such cancers are leukaemia (cancers of the blood), most types of lymphoma (cancers of the lymphatic system) and cancer known as myeloma (cancer of a certain type of cell in the bone marrow). [2,3]

How cancer spreads

Some cancers spread by direct extension, whereby abnormal cells literally grow into nearby organs or tissues. [4]

Other cancerous cells, as they continue to divide and multiply, may cause damage to or infiltrate blood vessels and thus be carried to distant organs via the bloodstream. The lymphatic system, which is considered to be the body’s disease-fighting network, may also inadvertently carry cancerous cells to other parts of the body. In this new location, cancer cells may grow and form new tumours – these are called metastases. [2,3,4]

If cancer cells spread via the bloodstream, metastases can often be found in the bones, liver, lungs, or brain. It is, however, always named after the organ or area where it first began. For example, if colon cancer spreads to the liver, it is called metastatic colon cancer, not liver cancer. [2,3]

What causes cancer?

Genes inherited from one's parents

Exposure to cancer-causing agents

Smoking tobacco or drinking too much alcohol

Too much exposure to sunlight

Cancer cells are able to grow and multiply uncontrollably because of multiple changes in their genes. There are many possible causes, or risk factors, for such changes, including genes inherited from one’s parents, or exposure to cancer-causing agents (such as some chemicals or asbestos) in the environment. Other risk factors include smoking tobacco or drinking too much alcohol as well as too much exposure to sunlight. Certain viruses are linked to an increased risk of developing cancer, such as the human papillomavirus. Very often there is no obvious cause. [3,5]

Cancer is not contagious (it does not spread from one person to another), and it is not caused by being a bad person. [5]

Types of cancer

While all cancers arise from cells that have escaped normal cell division control mechanisms, they do not all behave in the same ways. They can differ in the way they grow, spread, or respond to treatment. While some cancers grow and spread fast, others grow more slowly. Some may respond well to treatment with chemotherapy or radiotherapy, while others may be more challenging to treat. [3]

There are more than 200 different types of cancer, each with a specific name, targeted treatment, and a different prognosis (chance of being cured). [4]

We broadly distinguish the following types of cancer:


These malignant tumours originate from cells lining the surfaces of the body, such as from the stomach lining, cells lining the breast milk ducts, or cells lining the airways. We often refer to them just as cancers, e.g., stomach cancer, breast cancer, or lung cancer.


Sarcomas are malignant tumours that originate from cells that occur in structures that provide support to the human body, e.g., bones, muscles, or cartilage.

Blood cancers

These cancers do not form tumours (or lumps) but arise from cells within the bone marrow or blood. [4]

Cancer treatment

Treatment of cancer has become well advanced. There was no cure or treatment in ancient times, whereas today, medical science offers different therapeutic options specifically targeted to the type of cancer present. [1]

In some instances, surgical removal of the tumour may be curative. In other instances, surgery may not be appropriate or may be combined with chemotherapy and/or radiotherapy (radiation therapy). Today hormonal treatment has greatly facilitated the treatment of breast and prostate cancer, whereas immunotherapy has greatly improved the prognosis of previously difficult-to-treat cancers. With immunotherapy, monoclonal antibodies are used to help combat cancer. A monoclonal antibody is produced by cloning a unique white blood cell so that all subsequent antibodies derived this way can be traced back to a unique parent cell. Some such antibodies are designed to interact with specific targets on the cancer cells so that the body’s immune system is better able to recognise and destroy these abnormal cells. [1,6]

Towards the end of the 20th century, targeted therapies like growth factor inhibitors or anti-blood vessel formation medicines (that deprive the tumour of its blood supply) also became available. [1]

Today studies are also being done with vaccines that boost the body’s immune response to cancer cells. [1]


Cancer is an age-old disease that arises from cells dividing uncontrollably and that for the most part of human history was difficult, if not impossible, to treat. With recent advances in chemotherapy, hormonal treatment, as well as immunotherapy (that may specifically target the cancer cells involved) great strides, have been made in improving the overall prognosis of those diagnosed with this once-dreaded disease.


  1. Mandal, Ananya. 2019. Cancer History. News-Medical, viewed 22 June 2021, https://www.news-medical.net/health/Cancer-History.aspx.
  2. Cancer.Net. 2019. What is Cancer? American Society of Clinical Oncology (ASCO), viewed 22 June 2021, https://www.cancer.net/navigating-cancer-care/cancer-basics/what-cancer
  3. The American Cancer Society medical and editorial content team. 2020. What is cancer? American Cancer Society, viewed 22 June 2021, https://www.cancer.org/cancer/cancer-basics/what-is-cancer.html
  4. Irish Cancer Society. 2021. What is cancer? Irish Cancer Society, viewed 22 June 2021, https://www.cancer.ie/cancer-information-and-support/cancer-information/about-cancer/what-is-cancer
  5. Cancer Council Victoria. 2021. What is Cancer? – Information for people affected by cancer. Cancer Council Victoria, viewed 22 June 2021, https://www.cancervic.org.au/cancer-information/what-is-cancer
  6. National Cancer Institute. 2019. Monoclonal antibodies. NIH, viewed 23 June 2021, https://www.cancer.gov/about-cancer/treatment/types/immunotherapy/monoclonal-antibodies