The problem with folic acid and cancer is that for people with MTHFR, it doesn't process well, so there is Unmetabolized Folic Acid (UMFA) floating around in the bloodstream causing problems.
Ben Lynch has a new video on methylation and cancer that should be helpful.
http://seekinghealth.org/product/me...-cancer-in-prevention-treatment-and-recovery/
Breast cancer is one of the cancers caused by high estrogen, so measuring estrogen to verify that it's high, then if so, working on lowering estrogen might be helpful too. I don't know if that's considered to be more of a preventive measure or if it would also help for treatment.
If you've done 23andme testing, if you run it through the Detox Report on geneticgenie.org you can see if you have CYP1B1, which are SNPs which cause estrogen dominance. To lower estrogen, you can eat cruciferous veggies, or take supps with DIM or IC3, which are components of cruciferous veggies, or take calcium d glucarate.
There was also a lady interviewed by MTHFRsupport.com on their podcast who cured her breast cancer with Rick Simpson oil (cannabis oil).
http://www.blogtalkradio.com/mthfrsupport/2013/03/28/methylation-mthfr-and-cancer
There is supposed to be some kind of link between cannabinoids and methylation, but I haven't been able to get an answer out of MTHFRsupport yet.