done on the subject. this isn't the final word. critics point to earlier studies that found mammograms as being equititi equititive -- effective. sanjay, this absolutely grabbed my attention. and this statistic is why every one should care. every year, 37 million mammograms are performed costing about a hundred dollars per mammogram. >> yeah, and look, there's no question. there's a huge cost here. and the question for a long time has been what's the benefit to doing these and could there b a potential harm. this is a controversial topic. i've been covering this almost as long as i've been a medical reporter here on cnn. it is a long study, it is a large study. they looked at around 90,000 women.