OK, first let me state I am not a doctor, these are just the inferences I've gotten from my own experiences and from my interactions with other cancer survivors. So ask your doctor, but hopefully this can give you a little understanding :)

There are 2 things they typically take into account, first is stage. Generally speaking, the lower the stage, the less likelihood they will recommend chemo. Stage 0 or 1 is less likely to have chemo than 2 or 3.

Second is your cancer subgroup. If you are Triple Negative or HER2+, they seem to always recommend chemo. This is because these are the two more aggressive forms of breast cancer. They tend to spread more quickly and have a higher instance of recurrance. So they want to go guns blazing on treatment and throw everything at it.

If you are hormone positive, they tend to rely on something called an oncotype score. This is a predictor for recurrance. It tests the genomes (not genetics) of the cancer to determine the liklihood of recurrance. The score is from 1 to 100. Generally speaking, if your oncotype is less than 18, chemo may not be recommended. If it is between 18 and 30, it's generally up to you and your oncologist as the benefit of chemo is unclear. If it is above 30, they will most likely recommend chemo.

That is my understanding on how/when they recommend chemo. I hope that helps. Again, always as your doctor to explain it to you. Good luck!

the oncogene test will give a precertage as to the efficacy of chemotherapy. That helps to guide the oncologist in the selection of chemo vs radiation. The choices of chemo are cookbook style, you have a diagnosis confirmed with biopsy results and there is a standardized chemo regimen for that diagnosis. Most facilities will present cases at a tumor board, inwhich rad oncologists, surgeons and oncologists will decide the best course of action, so you get many opinions at the time. The decision is made uniformly, with the help of multiple studies over the years, and of course the oncology bible, national cancer consortium..a 800 page tome with all the cancers and all the regimens and the side effect and outcomes. When the onocologist in a big cancer hospital gives you their opinion, it is after all of this has occurred. Quality of life is taken inot consideration as well as the support systems in effect at the time. Social workers are there as well as oncolog nurses and any other ancillary voices that know the patient and the case.
So it is seldom one ides, but a consortium of ideas and recommendations

My oncogene test came back high end of low..I think in the 20s..so it was a toss up if chemo would have optimal effect for me. I wanted to be aggressive in chemo as I had chosen to spare the affected breast. I did have pos. sentinel lymph node involvement as well. So we opted for the 6 cycles of TAC and then later radiation. I did have one cycle of TAC and then wound up septic in the ICU. Having survived that one round, we decided to opt for radiation and arimidex of course. All my followup mammograms are negative and so far so good. Now looking back, would I make the same decision, probably not and I remember when I asked my collegues at work which they would opt for, the younger half said chemo and the older half said arimidex and XRT.
Equivocal either way.. It is a decision based on math and numbers and numerous studies, and I am confident my wizard of oncology was spot on when she pulled back when appropriate, and let me decide when to be aggressive when it was a true toss up. I thank her for that, allowing me an informed decision about my treatment, one with professional knowledge and input, yet stopping when needed as well. Seek council as needed, but the decisions must be yours..you will make the right one!

I was stage 1 er + and pr+ The her 2 is neg. At first they said I was her +. But I had 2 biopsies and 2 surgeries. They tested again and I was her2 -. My surgeon suggested Oncotype DX test. I went to my first chemo treatment and was told my test results whee finally in and I did not need chemo. I scored a 9. My understanding is any under 18 does not need chemo.

My score was 20 low intermediate...I am having radiation and on Arimidex..no chemo.. remember you make the decision on the treatment..what you feel is best for you...That is what the specialist at Fox Chase told me. I got 3 opinions on my treatment...good luck..