Testosterone makes prostates grow larger and makes prostate cancer grow more quickly.
I came across a study that looks at prostate size and testosterone levels:
Relationship between Serum Testosterone and Measures of Benign Prostatic Hyperplasia in Aging Men – Abstract
In our study, the serum testosterone levels in aging men did not correlate with the measures of BPH, including prostate volume and IPSS, regardless of whether total, free, or bioavailable testosterone was used. Age correlated with the measures of BPH, especially prostate volume. Additional large studies are needed to confirm these preliminary results.
To my surprise, patients with higher testosterone levels did not have larger prostates. As expected, patients with higher PSAs and older patients had larger prostates.