The human body is made up of trillions of cells, each containing genes that regulate growth, division, and cell death. Under normal conditions, cells grow, divide, and are replaced in an orderly process. 

Cancer develops when this process is disrupted. Abnormal cells begin to grow and divide uncontrollably and do not respond properly to the body’s normal regulatory signals. Over time, these abnormal cells can accumulate to form a mass of tissues known as a tumour, disrupting normal body functions. 

A tumour is a mass of abnormal cells that forms when cells divide more rapidly than normal or fail to die when they should. Tumours can develop in almost any part of the body and vary in size, growth rate, and behaviour. 

Tumours are generally classified into two main types: 

• Benign tumours are non-cancerous and usually remain localised. While they do not spread to other parts of the body, they may still cause health issues if they grow large or press against nearby organs or tissues. 
• Malignant tumours are cancerous and could invade surrounding tissues and spread to other parts of the body. 

Not all cancers form tumours. Some cancers, such as leukaemia, affect the blood and bone marrow and typically do not form solid tumours.

Metastasis refers to the spread of cancer cells from their original (primary) site to other parts of the body through the bloodstream or lymphatic system. This can occur even after the primary tumour has been treated or removed. Metastasis can affect distant organs and make cancer treatment more challenging. 

Identifying the specific type and origin of cancer is crucial, as treatment decisions are based on the cancer’s primary site, biological characteristics, and behaviour. Given the wide diversity among cancers, accurate diagnosis is essential to ensure appropriate and effective treatment.