Cancer is the name given to a collection of related diseases. It happens when normal cells in the body change and grow uncontrollably. These cells may form a mass called a tumour. A tumour can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body). In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissue.
Cancer can start almost anywhere in the human body, which is made up of a huge number of cells. In general normal cells grow divide and degenerate or die. But a cancer cell has a different life cycle altogether. Cancer cell growth is different from normal cell growth.
Instead of dying, cancer cells continue to grow and form new, abnormal cells. As cells become more and more abnormal, old and damaged cells survive when they should die, and new cells form when they are not needed and thus result in the formation of tumours. Over time, the tumours can invade nearby normal tissue, crowd it out, or push it aside.The process by which cancer spreads to the various parts of the body is known as metastasis. No matter where a cancer may spread, it’s always named based on the place where it first started. For example, breast cancer that spreads to and forms a metastatic tumour in the lung is metastatic breast cancer, not lung cancer.
Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common. Metastatic tumours can cause severe damage to how the body functions, and most people who die of cancer die of metastatic disease.
Cancer is named for the area of the body and the type of cell in which it started:
- Cancers that begin in the skin or tissue that covers the surface of internal organs and glands are called carcinomas.These include prostate cancer, breast cancer, lung cancer, and colorectal cancer.
- Cancers that begin in connective tissue—including muscle, fat, cartilage, or bone—are called sarcomas.
- Cancers that begin in the body’s blood-forming tissues—such as the bone marrow and spleen—are called leukaemia.
- These include acute lymphocytic leukaemia, chronic lymphocytic leukaemia, acute myeloid leukaemia, and chronic myeloid leukaemia.
- Cancers that begin in the lymphatic system (a network of vessels and glands that help fight infection) are called lymphomas. These include Hodgkin lymphoma and non-Hodgkin lymphoma.
Staging describes the extent or severity of a person’s cancer. It is based on the knowledge of the progress of the cancer within the body of the individual.
All cancers are staged when they are first diagnosed.
- The stage classification, which is typically assigned before treatment, is called the clinical stage.
- A cancer may be further staged after surgery or biopsy, when the extent of the cancer is better known. This stage designation (called the pathologic stage) combines the results of the clinical staging with the surgical results.
- The cancer stage designation doesn’t change based on the survival statistics and information on treatment by stage for specific cancer types but are based on the original cancer stage at diagnosis.