What else causes indents/dimple in breast?

I recently discovered a maybe nickle or larger indent on the inner side of one breast when I raise my arms. It's an uneven like shape, and hardly noticeable under regular overhead lights - I think anyway. I found it thanks to the lamplight I usually only use in the bathroom - it is very clear and definitely there then. I remember seeing a video where a doc said that dents are 'rarely caused by anything other than cancer' which I find hard to believe - but my online search for info to reassure me isn't really pulling up much info to dispute her. I'm hoping you all can suggest other things that may cause an indent?

I do have an appt for an u/s next month. I can't feel any noticeable lump, but if it's small it would blend in with my lump self lol. I have noticed I've suddenly been out breath a few times lately. Like sitting stationery and sudden coughing fit to catch my breath. Shoulder pain for a few years, but opposite side. Brain fog, which I blame on my kids stealing my brain cells. Ha.

Good luck to all!