I think this is the study. https://www.nejm.org/doi/full/10.1056/NEJMoa1612645
The significant part according to my oncologist was "residual cancer cells after treatment" - my triple negative tumour was resistant to something in the chemo mix I was given but oncology couldn't pin down exactly what. The key data for me in deciding was "rate of disease free survival was higher in the capecitabine group (82%)" and also "74% were alive and free from cancer at 5 years", a 10% and 5% improvement compared to the control group who didn't receive capecitabine.
I hate looking at statistics, who can say what part of the group I'll fall into? the 82% who do great or the 18% who get a recurrence despite all they do? I was incredibly lucky to find my cancer, although I certainly didn't feel lucky at the time. I had no symptoms and it was a totally random decision to get a breast screen - I had one at 50, I was going to turn 54 and thought I should just check because its free, so why not? A small triple negative cancer was found, in my surgeons opinion no more than three months old but already stage III.
I have young kids as we were only able to start a family with the help of IVF and I want to be around with them for as long as possible. So while my Dr tells me my odds of getting another triple negative breast cancer are the same as for someone who hasn't had one, the thought of going through another two year stint of chemo and operations frightens me. I don't have the gene but no one can say why I got this or that it won't come back and this time I or the scan miss it. I am hoping that if my luck turns and despite all tests to the contrary some cancerous cells migrated through my lymph system that the additional capecitabine has dealt with those. The mastectomy is for peace of mind (I think).