Preface

A malignant tumor is an actively growing tissue, composed of cells derived from a single cell that has undergone abnormal irreversible differentiation. These cells have two fundamental qualities: invasion and metastasis that induce the risk of cancer. Interestingly, recent researchers suggest that a malignant tumor is originated from cancer stem cells (CSC) accompanied with the niches. In this eBook, I would like to ask how the invasion and metastasis of cancer cells are explained by CSC theory and/or niche theory. The major points are as follows.

1. The fundamental aspects of cancer:
   1. The first point of discussion is about the CSC/ niche in carcinoma in situ lesion which appears in various types of cancer including breast and bladder cancers. Where is the niche corresponding to CSC in the above situation and what is the role of the niche in cancer progression?
   2. Cancer metastasis involves two characteristic occurrences: “organ preference metastasis” and “metastatic potential”. Can these metastatic characteristics be explained by CSC /niche theory well?
2. Metastatic phenotypes:
   • The mechanisms of cancer metastasis include non-invasiveness (carcinoma in situ), lateral/side invasion, stromal invasion, intravasation, circulation, arrest, attachment, extravasation, early growth, growth, and sometimes secondary/tertiary metastasis. This is followed by cellular/molecular mechanisms including cellular adhesion molecules such as carbohydrates, chemotactic activity by producing pseudopodia and invadopodia, deformability/plasticity and cytostreaming of metastatic cancer cells, and survival of metastatic cancer cells in floating (substrate-independent condition). Can these phenotypes of metastatic cancer cells be explained by cancer stem cell theory?
3. The goal of this study is clinical application of the knowledge obtained by CSC/niche theory. CSC/niche targets have important therapeutic implications. The role of CSC/ niche on therapies for the prevention, maintenance therapy, personalized care, and perhaps even integrative care of cancer will be discussed.