If, during the initial procedure, seemingly normal tissue is taken in an effort to get clear margins for either invasive cancer or DCIS, I use 19301. If only the abnormal tissue itself is being removed, I use 19125 (or if no localization, 19120). In either case, if a later return is required to get additional tissue for clear margins on CA or DCIS, I use 19301, with the 58 modifier if, as is usually the case, the return is w/in 90 days. I don't understand the point about the desk reference definition - if it's that the "mass" - or most of it - has already been removed, then 19120 seems LESS appropriate to me. Its actual CPT definition states cyst/tumor/lesion/aberrant breast tissue, whereas 19301 just states partial mastectomy, followed by some examples in parentheses. (I always have to put a note in my book: e.g.=for instance; i.e.=that is). So if most or even all of the additiional tissue removed turns out to be "normal", I can't see where 19120 is better than 19301. Just my opinion.
C.Martin CPC-GENSG