Which of the following is NOT an internal factor that can contribute to cancer?

Smoking is considered an external factor that contributes to cancer, as it involves environmental exposure to carcinogenic substances found in tobacco. In contrast, factors like genetics, hormones, and immune disorders are internal factors, as they are intrinsic to the individual's biological makeup.

Genetics refers to inherited mutations that can predispose individuals to certain types of cancer. Hormones can influence the growth of certain cancers, such as breast and prostate cancer, by promoting cell division. Immune disorders can affect the body’s ability to identify and eliminate cancer cells, leading to an increased risk of cancer development.

Recognizing the distinction between internal and external factors is crucial in understanding the multifactorial nature of cancer development.