answer:Okay. It took some detective work, but I think the short answer is: epilepsy actually kills more. If you trust this wikipedia table, epilepsy accounted for 0.22% of all human deaths worldwide in the year 2002. According to the American Cancer Society (you have to open the pdf on that page and search), breast cancer killed 465,000 people total in 2007. The same wikipedia page I linked before says that according to the WHO, there were 58,000,0000 deaths in 2005. So if you approximate that there were about 58,000,000 deaths in 2007 as well, that gives you: 465,000 breast cancer deaths / 58,000,0000 total deaths = 0.008% So, 0.22% (epilepsy deaths) > 0.008% (breast cancer deaths). I imagine these prevalence rates change depending on whether you’re looking at developed countries and access to treatment. I suspect breast cancer represents a lower proportion of global deaths simply because in many countries, women are unlikely to live long enough to get it.