I have read that you lose muscle mass when you begin HRT. I currently have a 39" chest and am wondering how much I can reduce that with when I start Hormones.

If you're talking about male-to-female hormones aka estrogen, then yes you would probably lose muscle mass, unless you were actively working out to keep that muscle mass.

This is a zombie thread folks - nothing here to see.
I've reposted the newer content here https://www.susans.org/forums/index.php/topic,191304.0.html