ABSTRACT
Introduction Malignant tumors consist of cancer cells and tumor-associated host cells. The interaction between the two categories of cells influences invasion and metastasis, as proposed in 1889 by S Paget. He stated that the microenvironment of each organ, the ‘soil’, influences the survival and growth of the cancer cells, the ‘seed’. This ‘seed and soil’ theory is broadly supported by clinical observations:
■ Although metastasis starts early, it may become apparent many years after removal of the primary tumor (e.g., bone metastasis from breast cancer and liver metastasis from ocular melanoma).
