I did a quick google and found a couple of articles. A study was done at the Univ of Washington (where the MDR1 mutation was discovered) in 2001. They believe only about 1% of BC's are carriers of the mutated MDR1. Also, in 2006, 362 BC's were tested at UC Davis, and only 1 had the mutated gene. It's pedigree was unknown, so it was not included in the results. I guess that should make me feel better about ivermectin, but it still nags me a little.