Breast Reduction from 500cc to 400cc?

In order to see a significant change in breast size, it is likely that you will need to downsize breast implants at least 100 mL. In other words, the change of 40 mL may be a waste of your time/efforts.

 Whether or not additional breast lifting will be necessary, will depend on your physical examination. As you know, if you end up with loose/"sagging" skin after the downsizing of breast implant procedure, the overlying skin “envelope” will need to be tightened. You may want to give your plastic surgeon  your consent to revise your breast lift if necessary, at the time when you undergo downsizing of breast implants.

 I hope this, and attach link, helps you as you learn more about revisionary breast surgery.

Best wishes.

If you really think your breast implants are too large reducing them by 40 to 100 mL doesn't make much sense. They really will be that much of a

Volume of implants much less important than dimensions.  When you reduce to 400, will this be a reduction in projection, in width, or both? How much of your breast volume is implant?  If your implants occupy half your breast volume, then a 20% reduction in implant volume (500 to 400cc) represents a 10% reduction in breast volume.  Will this be enough to make you happy?  Whether or not you will sag depends on several factors including skin elasticity, difficult to evaluate online.