Is testosterone bad for the immune system or cancer causer?

The dose makes: The poison. Reasonable doses as prescribed by a physician are safe. When used improperly, there may be an increased risk for prostate cancer in men. It should not affect the immune system.

No: Optimizing testosterone levels into old age is a good thing. High normal testosterone levels correlate with lower risk incidence of prostate cancer, diabetes, and heart disease. Testosterone does not cause prostate cancer. But if someone has a prostate cancer that hasn't been diagnosed, then using testosterone can feed the cancer.