Tumor -budding-, which is focused on in this book, is generally defined as an isolated single cancer cell or a cluster composed of a very small number of undifferentiated cancer cells in the stroma of the actively invasive front. The correlation of tumor budding with clinical outcome in colorectal cancer was first reported in the 1980s by Japanese surgeons. Since then, the clinical usefulness of this finding in colorectal cancer has been recognized in many countries. Its usefulness has been clarified not only as a prognostic factor and a potential parameter for a grading system, but also as...