alex ortiz in cairo has more on the growing influence in north africa. >> reporter: the latest isis videoivered a clear and direct threat to christians in the middle east. >> you will not have safety, even in your dreams, until you embrace islam. >> reporter: then militants carried out what appears to be a mass execution. masked men lined up two groups of ethiopian christians, shooting some captives and beheading others. still, isis claimed that christians who pay a tax to live in its territories are well- treated and called on christians who have left isis-controlled land to return. in the same video, this man is identified as a christian who said he's safe and happy living under the islamic state. but isis has a well-documented history of targeting religious minorities in syria and iraq massacring civilians and desecrating churches. this is the second mass execution of christians in libya isis claims to have carried out this year bringing their campaign of terror to the shores of alex ortiz, cbs news, cairo. >> glor: we've long been told aspirin can help reduce heart disease. now a new

alex ortiz, cbs news, cairo. >> glor: we've long been told aspirin can help reduce heart disease. a new study says long-term regular aspirin use can substantially cut the risk of some kinds of cancer. here now to explain is dr. heather yeo of new york presbyterian-weill cornell medical center. doctor, good to see you. why was this study so significant? >> thanks, jeff. actually, the study is important because it's one of the first studies to study patients, 130,000 patients actually, for such a long period of time. they studied patients for over 32 years and showed that after taking a moderate amount of aspirin for a long period of time, patients had a significantly decreased risk of cancer. >> glor: gastrointestinal and colo-rectal cancers? >> correct. and in fact, for gi cancers, the risk goes down by 20 percent, and for colo-rectal cancers, for patients i treat in particular, it goes down by 25%. so that's really exciting news. >> glor: but the duration, it did say, what, 16 years, before it is effective in this way? >> correct. patients need to take the aspirin for at least 16