I don't have any personal experience, but here is an excellent article:
Mammary Gland Tumor in Dogs | petMD
The tumors are malignant in about 50% of the cases. Surgery is the recommended treatment, as well as spaying if the dog has not been spayed yet. If it were me, I'd get the surgery, although I have to do more thinking about whether I wanted the tumors removed individually, or whether to get the mastectomy. I'd first try to see a board certified veterinary oncologist and see if they can determine whether the tumors are malignant first.
Here is a link for locating board certified veterinary oncologists. There are many in Ohio:
Locate A VCS Member