How does naturally occurring testosterone relate to prostate cancer?

Testosterone itself is not likely to increase a person's risk of developing prostate cancer. As with many cancers, the exact cause isn't clear. But many prostate cancers are sensitive to testosterone, meaning that testosterone can help cancer cells grow and multiply.

For many years, people believed there was a one-to-one relationship between testosterone levels and cancer growth — the higher the testosterone levels, the greater the growth of prostate cancer. But newer research has shown that this isn't entirely true.

Scientists now think that testosterone levels promote prostate cancer growth but only up to a certain point. One theory that helps explain this is called the saturation model. It says that prostate cancer cells only need a certain amount of testosterone to grow. Once they reach that level, adding more testosterone doesn't make much difference. So while testosterone is important for cancer growth, it's not the sole driver of prostate cancer.