I am not terribly impressed by the relationship between bras and breast cancer if it exists at all. however i do think that free movement is valuable in sustain internal health. The flesh is constantly massaged by motion movement all of which prevents local issues.
Thus the advice here is good and we will leave it at that.
If it is in fact practical or not is an individual issue. Even if there were a serious biological pathway to be concerned about, most would ignore it and continue on.