Tumor or cancer is an insidious disease that results from an uncontrolled growth of abnormal cells in part(s) of the body. There is a burgeoning interest from health professionals and the general public in learning about tumor/cancer mechanisms, clinical features, diagnosis, treatment, and prognosis. Depending on the types of tissue involved, tumors/cancers are grouped into a number of broad categories: carcinoma, sarcoma, leukemia, lymphoma, myeloma, melanoma, central nervous system cancers, germ cell tumors, neuroendocrine tumors and carcinoid tumors. Prognosis for a given tumor/cancer is usually dependent on the location, type, and grade of the tumor, patient's age and health status. The completion of the Human Genome Project in 2003 and the establishment of The Cancer Genome Atlas in 2005 have offered promises for better understanding of the genetic basis of human tumors/cancers and have opened new avenues for developing novel diagnostic techniques and effective therapeutic measures.