Hi - I think probably your mom's doctor referred to "poorly differentiated" cells in her biopsy; this is just a way doctors refer to cancer cells, and how aggressive they might be. Poorly differentiated means they're more rather than less aggressive; but then, most cancer cells are.

It's not unusual for a run of clear mammograms to be followed by a  suspicious mammogram, then a biopsy, then a cancer diaagnosis; that's how it goes for most women with breast cancer. The radiologist must have determined that the tumor is large enough to warrant a mastectomy, but I'd urge you and your mom to get more information before surgery. Does she really need a mastectomy, or would a lumpectomy be a possible choice?

Please read our post on invasive ductal carcinoma (which is probably your mom's diagnosis). I hope it'll give you a better idea of what you and she will be dealing with. Best of luck to you - PJH