I don't know the stats on what proportion of patients who present with dimpling actually have breast cancer.  I would guess that your doctor is speaking of her experience in her practice.  If she sees lots of patients with dimpling who don't have cancer, that should be very reassuring.

I always assumed that when doctors use the words dimpling to describe a breast cancer symptom, they meant an indentation caused by a lump that is pushing out in one place, causing a dimple somewhere else.  With that type of dimpling, a cyst or any other type of benign growth can cause a dimple, but not be cancer.  I found out in my own experience that that is only one type of dimpling associated with breast problems.

Another type of dimpling is caused by swelling in the breast.  As the skin swells, not all of the connective tissue swells, which leaves the skin looking pitted and dimpled like the skin of an orange.  This type of dimpling is one symptom of a dangerous form of breast cancer called inflammatory breast cancer.  However, other causes of swelling like an infection, or even pregnancy or other hormonal changes can also cause this kind of dimples.

So while I don't have exact statistics, your doctor's attempts to reassure you are on target.  You will want to be assertive about following up with all testing until you are sure you know what is causing the dimpling because it might be dangerous, but it is much too soon to panic.  Good luck with the ultrasound.