Cancer is a disease that starts in our cells. Our bodies are made up of millions of cells grouped together to form tissues and organs, such as muscles, bones, lungs and liver. Genes inside each cell order it to grow, work, reproduce and die. Normally, our cells obey these orders and we remain healthy. But sometimes the instructions get mixed up, causing the cells to form lumps or tumours, or spread through the bloodstream and lymphatic system to other parts of the body.
Tumours can be either benign (non-cancerous) or malignant (cancerous). Benign tumour cells stay in one place in the body and are not usually life-threatening. Malignant tumour cells are able to invade nearby tissues and spread to other parts of the body. Cancer cells that spread to other parts of the body are called metastases.
The first sign that a malignant tumour has spread (metastasized) is often swelling of nearby lymph nodes, but cancer can metastasize to almost any part of the body. It is important to find malignant tumours as early as possible.
Cancers are named after the part of the body where they start. For example, cancer that starts in the bladder, but spreads to the lung is called bladder cancer with lung metastases.
Source: Canadian Cancer Society