First off, mean mommy should stand corrected, by not masturbating will not cause testicular cancer. By not regularly masturbating, fluids normally produced by the testicals and not expelled by masturbation or intercourse, will be flushed out of the body within the urine. Also, the prostate produces a fluid that combines with the sperm at time of release out of the body. As an old addage goes, 'Use it or lose it' , by not having regular sex or masturbation, can cause problems with the prostate, sometimes leading to prostate cancer.
So do not let anyone tell you otherwise, if you feal in doubt, search the internet for a wide variety of information on sexual health from medical sites or if you feel comfortable, see a health professional. In other words, do not feel like you are a monster for doing the deed, it is part of healthy body functions. So just enjoy what you do and how you are doing it.