Wonder where that statement came from? Well, one of the comments I’ve heard about mastectomy bras is the issue of the bra sliding up as there is nothing to hold it down and in place.
Other issues are the need for a soft, comfortable fabric, some stretch, and no side seams to irritate scar tissue. Finding the right bra for your situation can be a challenge
Here is one with a long line that hugs the torso providing the ‘anchor’ for your bra. Worth having a peak at this style of mastectomy bra, as well as others to see what works for you.