Well, a breast prosthesis is outside the envelope of the skin, so I have no doubt that from accounts and descriptions, they can see it. Apparently, however, it pulls as an "anomaly" in the AIT scanners since it's something other than human flesh, and given the social sensitivity to difference present in the average TSA agent, well...it seems to create problems.
I don't know how it works for implants; I'd think that since the scanner apparently sees the edges of human skin that it wouldn't detect an implant. I know that even though I had the skin-sparing mastectomy, which gives me a chest akin to a 12-year-old boy's, there's no real technology for implants. I would personally prefer not to have implants anyways, but that's just me.
Of course, this dredges up a troubling thought: people could have things implanted within the envelope of the skin. I know that these AIT scanners don't really protect anyone, but I do know that they're being used as an excuse to harass women with prosthetic breasts; I'd imagine that the 30% of us who stuff our bras somehow in another manner thus generate attention from your TSA friends.
It's sad that we've come to the point that basically being female generates additional scrutiny, given that a maxi-pad seems to be another thing that generates "anomalies."