Cancer is a group of several hundred diseases in which abnormal cells are not destroyed by normal metabolic processes but instead proliferate and spread out of control. Cancers are distinguished from each other by the specific type of cell involved and the place in the body in which the disease begins.

Tumours can be benign (not a cancer) or malignant (a cancer). Benign tumours do not invade other tissues or spread to other parts of the body, although they can expand to interfere with health structures. The main features of a malignant tumour (cancer) are its ability to grow in an uncontrolled way and to invade and spread to other parts of the body (metastasise).

The registration of cancer is required by law, usually under the Public Health Acts, in each State and Territory. These registries report in various formats on cancers in their respective jurisdictions and supply information for national collation through the National Cancer Statistics Clearing House (NCSCH).

Although there are hundreds of different cancers, there are five major categories: carcinoma, sarcoma, myeloma, leukaemia and lymphoma. There are also some cancers of mixed types.

• Carcinoma: Malignancy (ie cancer) of the internal or external lining of the body. For example, squamous or epidermoid carcinoma of skin, lip, tongue, cervix.
• Sarcoma: Malignancy of connective tissue origin. For example, bone, cartilage, skeletal muscle, fibrous tissue, neurongenic connective tissue.
• Myeloma: Malignancy of plasma cell series (cells which produce some of the proteins found in the blood). These cells are generally found in the bone marrow.
• Lymphoma: Cancer of cells of the lymph nodes or of similar cells which may occur elsewhere.
• Leukaemia: Malignancy of the blood-forming elements of the bone marrow.
• Mixed types: Cancer composed of different tissue types. The type components may be within one category or from different categories.

A cancer registry can be defined as an organised system for the collection, storage, analysis and interpretation of data on persons with cancer. Each state and territory in Australia maintains a cancer registry. A national minimum data set from the state and territory registries is provided to the National Cancer Statistics Clearing House to enable national trends in cancer to be monitored.