Help with treatment plan!!

FindingACure88

My mom was 14 years in remission from stage II lobular breast cancer when she found an axillary mass on the side of her mastectomy. Prior to her surgery a full bodyPET scan was completed which showed that cancer was contained to the right axilla only, praise the Lord. She is 54 years old and otherwise completely healthy.

She had a right axillary lymphadenectomy where they removed a large (7cm)tumor with extensive matting of lymph nodes. The entire tumor was successfully removed along with 3 other surrounding lymph nodes, all of which were positive for cancer.

Pathology showed she is ER positive, however only 15%. She is PR negative and HER-2 negative. Her Ki-67 score was 20%, and her genetic panel came back negative

After meeting with her oncologist, it was decided that she would undergo 6 weeks of radiation, starting 3 weeks post op. After this she will be taking a hormone pill.

My question is, does it seem odd that she will not receive chemo? Her oncologist was very optimistic saying it wasn't indicated because the cancer was so well contained. However, I'm nervous by the node involvement. Does his confidence come from the clear PET scan? Doesn't 15% ER positive seem like a low percentage? I truly trust her doctor as he spent his residency at MD Anderson, but I want my mom to have the best possible treatment plan. Any advice or input is appreciated!