A group of tumour cells in an area near the primary (original) tumour. In melanoma, satellite tumours occur within 2 centimetres of the primary tumour, on or under the skin, and can be seen without a microscope. Satellite tumours may also be found in other types of cancer, including cancers of the breast, lung, liver, and brain. Having a satellite tumour is a sign that the cancer has spread from where it first formed1.