Answer
One experiment would be to used cultured prostate cancer cells, some left alone and other treated with estrogen to see if estrogen does have a stimulatory effect. Another would be to treat some prostate cancer patients (starting with animal models) with estrogen-blocking chemicals to see if prostate growth slowed.
Work Step by Step
There are other possible experiments, but any experiments need to test estrogen treatment with non-treatment or non-treatment with a blocking of estrogens.