A new paper is questioning a decades-old Canadian breast cancer screening study and calls for changes to Canada's guidelines, allowing more women in their 40s to be routinely screened. Watch The National live on YouTube Sunday-Friday at 9 p.m. ET Subscribe to The National: https://www.youtube.com/user/CBCTheNational?sub_confirmation=1 Connect with The National online: Facebook | https://www.facebook.com/thenational Twitter | https://twitter.com/CBCTheNational Instagram | https://www.instagram.com/cbcthenational More from CBC News | https://www.cbc.ca/news The National is CBC's flagship nightly news program, featuring the day's top stories with in-depth and original journalism, with hosts Adrienne Arsenault and Andrew Chang in Toronto, Ian Hanomansing in Vancouver and the CBC's chief political correspondent, Rosemary Barton in Ottawa.