Welcome to the land of bizarre in PCa and especially for us patients whom are using hormone therapies in our journey. Certain drugs including: casodex (and its equals), estrogenic drugs like: DES, emcyt, estradiol patches and perhaps some other select drugs in fighting PCa can give some men possible breast enlargement. Hey I am not making this up, it is for real and there are choices to counter the enlargement and/or tenderness issues that can occur.
Drug methods: arimidex, tamoxifen, exemestone, raloxifene (can be used to prevent such or help with tenderness issues, you have to research that for yourself)
Radiation method: you can get a 'light duty' radiation proceedure to your breasts that does stop enlargement or for people that already have enlargement you can still elect to get this before they could get larger, BUT...once you have enlargement you are staying at whatever level upon starting this. I suppose there are even surgecial methods to deal with comestically in effect reduction or return to the normal look, as plan B for men.
Here is the radiation program: uses electron rays (light duty compared to neutron, proton, photon) rad-doc can control depth so as not to hit your heart with rays and this is lesser ray category. Now it is usually done in 3 sessions for patients whom do this but it can be done in one session by experienced skilled radiation doc (maybe not the new guy out of college 
). Normally you get 12 gy (gray scale) exposure split into those 3 sessions equally, so 4 gy and quick and fast exposures.
The fast lane method: 10 gy given at once with electron rays at 3.5 minutes per 'boob' and it covers about 6" dia (nipple being center point), math majors that is about 3" radius (LOL).
The aftermath: it is similar to seeing a sun burn ring around your breasts about 6" on each side, naturally you look in the mirror and say darn I hope this goes away, ring around the collar is one problem, this one!!!! Well it goes away and you look normal, but it might take 3-4 weeks so don't go to the beach like this, unless you need comedic relief and you would find alot of laughs I would guess. 
Did I ever mention PCa can resemble the Twilight Zone??