The creatine would be fine as long as you did not take as directed the reason I say this is because it will cause you to hold water when taken as directed.
I recomend that you take it in the middle of practice and at the end but with no "loading of the creatine" Simply watch your weight if it goes up in 2-3days you are taking too much and you will be slowed down.
As for AAS aka steroids there are no studies linking it to cancer of any sort, the fact of the matter is that satisticly multivitamines are more dangerous.
Are they toxic? Depends on how you take them, I've seen modles do on carot only diets and end up with jondus and negative effects on the whole body system and end up spending weeks in the hospital.
Also people can die from just simply drinking way too much water.
There are stupid people every where and that is what is toxic.
Women take hormones/steroids each and every day and everyone is fine with it, and we know what taking these factually (with unlimited studies to back it up) cause breast cancer, ovarie cancer, various blood vessel dissease that lead to heart atack and stroke ect. Some women take these drugs to get larger breast or to look yonger ect.
There are far far worse things in everyday life that people think are safe for them that are worse than stroids.
With that said steroids are not going to help anyone in tennis at all to any degree especially something such as Dianabol that is going to make you hold water and increase blood pressure to an extent that you will not be able to hang with your usual opponets on the court.
Tennis is not about strength it is about skill and technique, most of the men here can't even do what the pro women do, do why would you be woried about being extremely strong beyond what is naturally obtainable?
GOAT = Novak (Son of God)> Fedal