Cancer

Cancer is not a single disease but a broad term for a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues. The key to understanding cancer lies in realising that it is fundamentally a failure of the normal controls on cell division.

What is Cancer?

Normal cells in the body grow, divide, and die in a controlled, orderly way. This process is tightly regulated by genes. Cancer begins when a single cell's DNA is damaged, producing a mutation. This mutation affects genes that control cell division — specifically, proto-oncogenes (which promote growth) and tumour suppressor genes (which inhibit growth).

When a proto-oncogene is mutated, it becomes an oncogene — a permanently "on" growth signal. When a tumour suppressor gene is damaged, it can no longer put the brakes on cell division. The result is a cell that divides uncontrollably, producing a mass of abnormal cells called a tumour.

Types of Tumours

Not all tumours are cancerous. The textbook distinguishes two main types:

• Benign tumours: These tumours remain confined to their original location. They do not invade surrounding tissues or spread to other parts of the body, and cause comparatively little damage.
• Malignant tumours: These are the true cancers. Malignant tumours are masses of cells that grow rapidly, invade and destroy the tissues around them, and can break away. The process by which cancer cells break off from the primary tumour, travel through the blood or lymph system, and form new tumours in other parts of the body is called metastasis. This ability to spread is what makes malignant cancers so dangerous and difficult to treat.

Causes of Cancer

The textbook classifies the agents that cause cancer (carcinogens) into three broad categories:

1. Physical agents: These include ionising radiations like X-rays and gamma rays, and non-ionising radiations like UV rays. These radiations can directly damage DNA, causing mutations.
2. Chemical agents: The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer.
3. Biological agents: Some viruses can cause cancer. These are called oncogenic viruses, and they carry genes known as viral oncogenes. Several genes called cellular oncogenes (c-onc), or proto-oncogenes, have also been identified in normal cells — under certain conditions these can be activated and lead to the oncogenic transformation of the cell.

Detection and Diagnosis

Early detection is critical for successful treatment. The textbook mentions several methods:

• Biopsy and Histopathological studies: A small piece of the suspected tissue (a biopsy) is removed and examined under a microscope by a pathologist. This is the most definitive way to diagnose cancer.
• Blood and bone marrow tests: These tests can reveal abnormal numbers of white blood cells (as in leukaemia) or other markers.
• Imaging techniques: X-rays, CT scans (computed tomography), and MRI (magnetic resonance imaging) are used to locate tumours and see if they have spread.
• Antibody-based tests: Antibodies raised against cancer-specific antigens are also used for the detection of certain cancers.
• Genetic-susceptibility testing: Techniques of molecular biology can detect genes in individuals with an inherited susceptibility to certain cancers. Identifying such genes can help in prevention — a person found to carry one may be advised to avoid exposure to the specific carcinogen they are susceptible to (for example, avoiding tobacco smoke where there is a genetic susceptibility to lung cancer).

Treatment of Cancer

The textbook outlines the main approaches to cancer treatment, which are often used in combination:

• Surgery: The physical removal of the tumour. This is most effective when the cancer is localised and has not metastasised.
• Radiation therapy (Radiotherapy): Tumour cells are killed by exposing them to high-energy radiation (like X-rays or gamma rays). The radiation damages the DNA of the cancer cells more than that of normal cells because cancer cells divide rapidly and are less able to repair the damage. …