The law of Bergonie and Tribondeau is that the radiosensitivity of a biological tissue is directly proportional to the mitotic activity and inversely proportional to the degree of differentiation of its cells. This law underpins the field of radiation-oncology, although such a general law may not apply precisely in all cases.
Usually neoplastic cells are more radiosensitive than the cells from which they originate; in fact, they reproduce much faster than healthy cells.
Cellular differentiation describes the extent to which a tumor resembles the normal tissue from which it derives. The more it differs from healthy tissue, the greater its radiosensitivity will be.