I Am 45 Years Old And Have Had A Right

I am 45 years old and have had a right mastectomy for a grade 2 multifocal lobular cancer with largest area 3.5 cm. ER pos, PR pos and HER neg. No lymphovascular invasion and SLNB negative. No LNs involved. It is also a luminal B tumour. I saw an oncologist who felt I needed chemo but she was sending off the oncotypedx and she said she would not base her decision on this report solely but would use it maybe to give lighter course of chemo. The report came back at 11 and she immediately stated no chemo at all just based on the report. I was also found to be postmenopausal. I'm worried about the tumour size, my age , luminal B and multifocal tumour , can oncotypedx be trusted solely. She is putting me on arimidix after a DEXA scan. She gave me no percentages on prognosis etc and no discussion or choice. Would you be worried about not getting chemo ?