What is cancer and malignant tumors?

The global and national scientific communities of oncologists worked out a universally acknowledged definition of cancer and other malignant tumors that sounds in the following way: cancer is a genetic disease of the nucleus of a somatic cell induced by a strong single or long-term systemic effect of carcinogens. What are carcinogens is discussed in the section where describe contemporary concepts of carcinogens.

Only those oncological diseases where the tumor develops from the cells of epithelial tissue are called cancer. For example, the glioblastoma multiforme, one of the most aggressive malignant tumors, cannot be referred to as brain cancer, because it originates from the glial cells. Consequently, the term brain cancer is incorrect.