Introduction

Cancer is a group of diseases characterised by abnormal cell growth through which cells may acquire the potential to disperse (metastasise) from the site of origin (primary tumour) to other sites in the body (secondary tumours). The word tumour comes from the Latin ‘tumor’ referring to the swelling that occurs as a consequence of these abnormal growths and is now used interchangeably with ‘neoplasm’, meaning new or abnormal cell growth. This definition of neoplasm leads to a major division of cancers into malignant and benign. The terms ‘tumour’ and ‘cancer’ have also come to be used synonymously but a distinction might be made in that metastatic cancer occurs because a tumour has acquired the capacity to invade its surroundings, the first step in spreading to secondary sites. This involves the destruction of other cells, critically some that make up the vessels of the circulatory (blood and lymphatic) systems. Once the tumour cell can get into the circulation it can be carried to other locations: it has become malignant. The implication, of course, is that there are tumours that are not malignant.