just thought this was interesting, and wondered if it extended to men (i assume it would).
I don’t know. Fibroblast growth factor can be relevant to breast cancer but might have no relevance to gynecomastia. It wouldn’t necessarily be the case that high FGFR1 activity reduces every effect of tamoxifen: it might only make a SERM a moot point with regard to cancer, causing estrogen-dependent cancers to act like estrogen-independent cancers.
It would take going through a great deal of stuff for me to be able to say what is going on there though: I’m not familiar with the mechanisms involved with various breast cancers or for that matter whether FGF has anything to do with gynecomastia. So the above is just to say that it doesn’t have to be case one way or the other: either way could be biologically possible.