It's called id papillary adenocarcinoma.
..The importance is whether it invades or confined to duct, and whether the margins are clear. These are analgous to dcis, usually er/pr+. They have excelent 5 and 10 year prognosis..Close to 100% survial, but it is when they are harbingers of invasive cancers that there are threats to life and breast. There are no clear causes.