Tumor also known as neoplasm is a mass of abnormal tissue that arises without obvious cause from preexisting body cells, has no purposeful function and is characterized by a tendency to have independent and unrestrained growth. Tumors are quite different from inflammatory or other swellings because the cells in tumors are abnormal in appearance and other characteristics. Abnormal cells, the kind that generally make up tumors differ from normal cells in having undergone one or more of the following alterations such as hypertrophy, or an increase in the size of individual cells; this feature is occasionally encountered in tumors but occurs commonly in other conditions; hyperplasia or an increase in the number of cells within a given zone may constitute the only criterion of tumor formation; anaplasia or a regression of the physical characteristics of a cell toward a more primitive or undifferentiated type; this is an almost constant feature of malignant tumors though it occurs in other instances both in health and in disease. This session discusses more about tumor pathology.