The term cancer encompasses over 100 different diseases. Each type of cancer has different causal factors, prognoses and treatments, but they all feature uncontrolled cell growth and the ability to spread locally or to other parts of the body (metastasis).
The main types of cancer are:
Carcinoma. Carcinoma is the most common type of cancer and initially develops in epithelial cells. These cells cover the external surface of the body (skin) and form the tissues that line internal organs (mucous membranes). If the carcinoma affects the surface of organs with a secretory function (e.g., tubules in kidney cancer, lobules in breast cancer, and so on), then it is known as an adenocarcinoma. If the tissue affected by the tumour does not have any glandular functions, it is called a squamous cell carcinoma or epidermoid carcinoma, as in the example of lung cancer or skin cancer.
Sarcoma. Sarcomas are cancers that form in the bone or soft tissues, including muscle, adipose tissue (fat), blood vessels, lymphatic vessels and fibrous tissues (e.g., tendons and ligaments).
Leukaemia. Cancers that originate in the blood-forming tissues found in bone marrow are called leukaemia. These cancers do not form solid tumours.
Lymphoma. Lymphoma is a type of cancer that initially develops in immune system cells, specifically in lymphocytes (T cells or B cells).
Multiple myeloma. This cancer forms in plasma cells, which are another type of immune system cell.
Spinal cord and brain tumours. There are different types of brain and spinal cord tumour. The name of each tumour depends on the type of cell and the site where the tumour initially develops in the central nervous system.
Difference between the terms cancer and tumour
Although many people believe the words cancer and tumour are the same, they actually have different meanings. Tumours may be either benign or malignant. In the case of benign tumours, the cells multiply in an uncontrolled manner, but without spreading to other parts of the body. Benign tumours are not usually life-threatening, but if they are not treated in time, they could transform into a malignant or cancerous tumour.
Metastasis. The spread of cancer
The type of cancer is always named according to the organ or tissue of origin, which is known as the primary tumour.
Cancer may start to spread by invading the surrounding tissues and/or penetrating the blood vessels and lymphatic system.
During this expansion process the tumour may spread to other organs or different locations in the same organ. This phenomenon is called metastasis.
Occasionally, the secondary metastases are identified before the primary tumour is diagnosed, while an analysis of the cell type may indicate the organ of origin.