There have been documented cases of breast growth through various methods; one is hypnosis/placebo (placebos, of course, basically being a form of 'self hypnosis), another through 'herbal' methods. (Which, personally, I believe to also be a placebo effect.) The biggest 'giveaway' for any sort of placebo effect, of course, being the extremely wide variation in results.
Interestingly, however, is work going on right now in Japan, using Lipotransfer technique. Literally, this is the injection of adipose (fat) tissue from one part of the patients body to her breasts! While there are still problems to be worked out, and a relatively small 'upper limit' for each individual procedure, the amazing thing about the final result is that, when it works perfectly, the adipose tissue is basically 'grafted' into the surrounding tissue of the breast. For all reasonable purposes, her breasts are 'real', as there is absolutely no foreign material in them! At this point, you could then perform a second procedure in order to increase size even more.
(See link below for more info)
http://www.cellport.jp/english/bust/
Interestingly, the first attempt at adipose-induced breast enlargement was by Vincenz Czerny... in 1895!