What is Cancer?

Cancer refers to a group of more than a hundred diseases that can originate in many different parts of the body.

However, the following features are common to all types of cancer:

  • Abnormal cell growth
  • Capacity to invade other tissues
  • Capacity to spread to distant organs via blood vessels or lymphatic channels (metastasis)

If cancer is left untreated, it can invade tissues, spread through the body and eventually lead to death.

Electron micrograph of a single breast cancer cell.
Electron micrograph of a single breast cancer cell.

How does cancer occur?

The body is made up of trillions of cells that usually grow, divide and die in an organized manner. This process is a tightly controlled by the DNA machinery within the cell. When a person is developing and growing up, cells divide rapidly to allow for growth but once adulthood is reached, cells mainly only divide to replace worn-out or dying cells or to repair injuries.

Cancer occurs when cells in a particular site start to grow out of control. Rather than dying, they continue to grow and form new, abnormal cells. These abnormal cells can also invade other tissues, a property that normal cells do not possess.

Molecular pathology of cancer

Cancer cells originate from normal cells in which the DNA (deoxyribonucleic acid) within the cell nucleus has become damaged or mutated.

DNA is the “blueprint” contained in every cell that carries instructions for the cell’s function, growth, death and protein synthesis. When this DNA becomes damaged, the cell usually either repairs the damage or dies.

However, in cancer cells, the damaged DNA is not repaired and neither does the cell die. Instead, it gives rise to many more abnormal cells that all contain the same defective DNA as the original cancer cell.

DNA damage may be inherited or it may occur spontaneously at any point in a person’s life. DNA damage can be triggered by exposure to certain toxins such as those present in cigarette smoke, for example. There are, however, multiple factors that can cause cancer and it is often difficult to pinpoint an exact cause.


As cancer cells proliferate, they eventually form tumors. Not all tumors are cancerous and capable of spreading. Those that are capable of spreading are referred to as malignant tumors. Benign tumors, on the other hand, do not invade other organs or spread to other parts of the body, although they can grow to a large size and start to press on surrounding organs and tissues.

Who gets cancer and how common is cancer?

There are millions of people worldwide who are living with cancer or have had cancer. Estimates suggest that around half of all American men and one third of all American women will develop cancer during their lifetimes. Healthy lifestyle factors can be adopted to help reduce the risk of cancer such as taking regular physical activity, maintaining a healthy diet and body weight and avoiding known risk factors such as exposure to tobacco smoke and too much sunbathing.

For some common cancers such as breast cancer and colon cancer, effective screening tests are available to help detect the disease as early on as possible. Early diagnosis and treatment initiation often improves the chance of a good response to anti-cancer therapy and therefore recovery.

Further Reading

Last Updated: Jan 30, 2020

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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