My mom is going thru chemo after lumpectomy, she noticed a lump in her other breast recently which showed probably benign in her mamo, is this a worry?

Only way to: know for sure is by biopsy. If it is read out as probably benign, biopsy can wait until she is finished with chemotherapy, because this is more important than worrying about something that is much less important.

Dr Hassell agreed

Probablecyst: If nodes neg after lumpectomy with adequate margins, lesion in other breast probably benign. This is confirmed on mammo, but dx required even if benign. That is fibroadenoma or cyst. After lumpectomy or mastectomy, remaining breast tissue constantly needs exam since cause of the Ca remains , such as MMTV virus. New lesion in remaining breast can appear at 1%/yr. for up to 15 yrs.

Dr Wang agreed

Not necessarily : it is and it isn't. If it wasn't there on her initial mammogram or the one with which she was first diagnosed with breast cancer, then it has grown despite being on chemo and it is absolutely worrisome and should be biopsied. If it has been there all along and hasn't changed, then it is likely not of concern