Q.Explain the different types of cancers.

Cancer is uncontrolled cell division; tumours are first classed as benign or malignant, and malignant (cancerous) tumours are further classified by the tissue of origin into carcinomas, sarcomas, and leukaemias/lymphomas.

Cancer results from a loss of the normal regulatory control mechanisms of the cell cycle, causing uncontrolled cell division and abnormal growth (a tumour or neoplasm).

1. Based on growth behaviour:

• Benign tumours: Cells remain confined to their original location, grow slowly, are usually encapsulated, do not invade neighbouring tissues, and do not metastasise (spread to distant sites). They are generally not life-threatening unless they compress vital organs, and are usually removable by surgery.

• Malignant tumours (true cancers): Cells divide uncontrollably, invade and destroy surrounding healthy tissue, and can metastasise - cells break away, travel via blood or lymph, and establish secondary tumours at distant sites in the body. These are far more dangerous and are what is commonly meant by "cancer".

2. Based on the tissue/cell of origin (types of malignant cancer):

• Carcinomas: Cancers arising from epithelial tissue (the tissue lining organs and body surfaces, e.g., skin, lungs, breast, colon). These are the most common type of cancer in humans.

• Sarcomas: Cancers arising from connective and supportive tissues, such as bone, cartilage, fat, muscle, and blood vessels (e.g., osteosarcoma of bone).

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