I stopped all hrt for 6 weeks before my surgery, as instructed.
My boobs got bigger (about 1 cup size, from A-cup to B-cup) albeit only temporarily, became very tender, and they began producing milk. Yep, I had lactating breasts for about 2 weeks. Then they kinda went back to how they were before (A-cup) and have stayed that way ever since. Once I restarted hrt after my op, I was hoping they'd get bigger again, but they didn't. A-cup it is.
The milk tasted very sweet BTW.
I didn't have any other effects from stopping the hrt.