Which of the following is NOT an internal factor contributing to cancer risk?

The correct answer highlights that chemicals are not considered an internal factor contributing to cancer risk. Internal factors, such as genetics, hormones, and immunologic conditions, originate from within the individual's body.

Genetics plays a significant role in cancer risk as inherited mutations can predispose individuals to certain types of cancer. Hormones can also influence the development and progression of various cancers, particularly those that are hormone-sensitive, such as breast and prostate cancer. Immunologic conditions, including those that affect the immune system, can impact the body’s ability to detect and eliminate cancer cells, thus increasing the risk for malignancies.

In contrast, chemicals are classified as external factors. These include carcinogens found in the environment, such as tobacco smoke, asbestos, and certain chemicals used in industries and agricultural practices, which can contribute to cancer risk when individuals are exposed to them. Therefore, the correct option distinguishes between the internal factors that originate from within the body and the external factors that arise from environmental exposures.