Cancer starts in the cells of our body. Cells are tiny building blocks that make up our organs and tissues. They divide to make new cells in a controlled way and only reproduce when needed.  They self-destruct when they are old or damaged.  This is how our bodies grow, heal and repair.  

Cancer develops when the normal workings of a cell go wrong and the cell becomes abnormal. The abnormal cell keeps dividing, making more and more abnormal cells – they ignore the normal signals within the body to stop dividing or to die. These eventually form a lump (tumour).  It is important to note that not all lumps/tumours are cancerous.  

Malignant (cancerous) cells can invade and damage surrounding tissue and spread to other parts of the body.  Benign (non-cancerous) tumours may grow large but do not spread to other parts of the body.  They can become problematic when they grow very large, are uncomfortable or unsightly, press on other organs, take up space inside the skull or release hormones that affect how the body functions. 

Cancers may be classified by their primary site of origin or by their histological or tissue types. 

Classification by site of origin 

By primary site of origin, cancers may be of specific types like breast cancer, lung cancer, prostate cancer, liver cancer, renal cell carcinoma (kidney cancer), oral cancer, brain cancer etc. 

Main subtypes: 

Carcinoma (lining of organs and tissue) 

– Squamous cell carcinoma (within squamous epithelium) and adenocarcinoma (originates within an organ e.g. liver/gland) 

– Basal cell carcinoma (base of skin) 

– Accounts for 80-90% of all cancer cases 

Sarcoma (connective tissue, bones, cartilage, fat and muscles) 

Leukaemia (blood and bone marrow) 

Lymphomas (in lymph and immune system) – types Non-Hodgkins and Hodgkins)  

Myeloma (plasma cells/white blood cells)