What term describes an agent that causes gene mutations?

The term that describes an agent causing gene mutations is "mutagen." Mutagens can be physical agents, such as radiation, or chemical agents that induce alterations in the DNA sequence. These changes can result in various genetic effects, including functional changes in genes, which may lead to various conditions, including cancer.

In contrast, carcinogens specifically refer to substances that can lead to cancer by causing mutations or promoting the proliferation of cells with mutations. Pathogens are organisms, such as bacteria or viruses, that can cause disease but do not inherently cause mutations in the DNA of their hosts. Teratogens are agents that cause malformation or abnormalities in a developing fetus but do not primarily function as mutagens. Thus, while each of these terms describes harmful agents, "mutagen" is the most accurate for the specific context of causing gene mutations.