The past twenty years have witnessed significant advances in the treatment of cancer by surgery and radiation therapy. Gains with cytotoxic chemotherapy have been much more modest. Of the approximately 900,000 newly diagnosed cases of cancer each year, 50010 result in death of the patient. The primary cause of these deaths is metastasis. Although the term metastasis was first coined by Recamier in 1829, only in the past ten years have there been intensive scientific investigations into the mechanisms by which tumor cells metastasize. What has emerged is a complex process of host-tumor cell interactions which has been termed the metastatic cascade. Due to the complexity of the metastatic process, the study of metastasis is multifaceted and involves elements of such areas as differentiation, en- zymology, genetics, hematology, immunology, membrane biochemistry and molecular biology. The major objectives of this book were to present the most recent advances in our understanding of how tumor cells metastasize to secondary sites by the leading experts in the biology of tumor invasion and metastasis. We hope that this book will lead to new concepts for the treatment of subclinical metastatic cancer. The chapters in this book address both the basic science of metastasis and potential clinical therapies directed toward interruption of the metastatic cascade or toward eradication of subclinical metastases. Many relevant topics have been omitted due to space considerations and thus the topics included reflect the prej- udices of the editors.