Baldwin has one key part of your answer testosterone is fuel for prostate cancer and adding it to your system may rekindle the cancer. Using it would be very risky and definitely should not be tried without approval from your oncologist (and then working carefully with him should you try it).
Unencumbered has another important part of the answer, though. Testosterone and estrogen are chemically quite similar and have some of the same impact on an ADULT body that has gone through puberty. Loss of testosterone in adult males or of estrogen in adult females results in the gradual loss of those features that are maintained by the appropriate sex hormone. Castration of an adult male (as for prostate cancer) results in gradual loss of body hair below the neck, hot flashes, reduction of libido, gradual shrinkage of adult male penis, loss of testosterone-fueled muscle mass, and, most importantly in your case, loss of protection against osteoporosis.
A LOW dose of estrogen not enough to feminize, and certainly not at the levels used for Male-to-Female transition may be sufficient to provide the protection against osteoporosis and also to ward off hot flashes.
There is also strong evidence that it can restore male-pattern sexual functioning. Erik Wibowo, a young neuroanatomist, worked with a population of male Wistar rats. Some were castrated before male rat puberty, some after puberty, and some left intact (though with genital surgery to provide equivalent surgical trauma). Given estrogen, those castrated before puberty took on female sexual behaviors and those castrated AFTER rat puberty regained male sexual functioning similar to that of the uncastrated rats. He has recently completed his PhD dissertation on the research.
I'm listing two of Erik's publications in medical journals below. You or your oncologist or urologist can either look for them or you can (once you've hit the magic FIVE Archive posts) send me a <Private Message> with an email address that will accept attachments and I will send you PDF copies of both of them. [The offer of PDF copies is open to any Archive member who wants to request them. I just need an email address to send them to.]
References:
Erik Wibowo, Paul Schellhammer and Richard J. Wassersug (2011).
unencumbered (imported) wrote: Sat Nov 16, 2013 5:46 am
Role of Estrogen in Normal Male Function: Clinical Implications for Patients With Prostate Cancer on Androgen
Deprivation Therapy.
Journal of Urology, Vol. 185, 17-23. DOI:10.1016/j.juro.2010.08.094
Erik Wibowo, Richard Wassersug, Karen Warkentin, Lauren Walker, John Robinson, Lori Brotto and Thomas Johnson. (2012). Impact of androgen deprivation therapy on sexual function: a response. Asian Journal of Andrology (2012) 14, 793794.