A key characteristic of the adaptive response of cells is that if the stimulus is removed any alteration in cell growth reverts to normal. In contrast to these reversible adaptive responses certain stimuli cause changes in genetic material that result in permanent alteration of the normal cellular growth pattern. Such altered cells, which are termed neoplastic, fail to respond normally to signals controlling the cell growth. They proliferate excessively in a poorly regulated manner, forming a lump or tissue mass called a neoplasm. A tumour is said to be benign when its microscopic and gross characteristics are considered relatively innocent, implying that it will remain localised, cannot spread to other sides. Malignant, as applied to a neoplasm, implies that the lesion can invade and destroy the adjacent structures and spread to distant sites (metastasize) to cause death. Mechanisms by which metastatic cells arise from primary tumours and why they metastasize to specific organs can be explained by cross talk between selected cancer cells (the ‗seeds‘) and specific organ micro environments (the ‗soil‘) implying that Stephen Paget‘s 1889 seed-soil hypothesis. Metastasis of a tumour cell depends on its interactions with the homeostatic factors that promote tumour cell growth, survival, angiogenesis, invasion and metastasis.