Hi,
I also experienced some water weight gain(had puffiness in ankles) the first couple years on Herceptin. I eventually asked my Onc to prescribe a mild diuretic and that helped alot. I have since weaned myself off of it and try to stay physically active. Seems to be working, cause my weight doesn't fluctuate much at all anymore and I am basically at my pre-cancer weight (except for the annual holiday weight gain!). So maybe it just takes time for our bodies to adjust to the Herceptin
Kim in CA