What is the term for a substance that can induce tumors in living tissues?

The term that refers to a substance capable of inducing tumors in living tissues is "carcinogen." Carcinogens are agents that can cause cancer by altering cellular metabolism or damaging DNA in cells, which leads to uncontrolled cell growth and tumor formation. It is essential to recognize that carcinogens can be found in various forms, including chemicals, radiation, and certain viruses.

In understanding the context of this question, it is helpful to differentiate carcinogens from the other terms. A mutagen, for example, is a substance that causes changes or mutations in the DNA sequence of an organism. While some mutagens can lead to cancer, not all mutagens are carcinogenic. An oncogene refers specifically to a mutated version of a gene that has the potential to cause cancer, but it is not a substance itself. Lastly, a teratogen is an agent that causes malformation or abnormalities in a developing embryo or fetus, rather than inducing tumors in already developed tissues.

Thus, "carcinogen" is the most accurate term among the choices listed, as it directly pertains to substances that promote tumor development in living tissues.