Such tumors are common in dogs, and are usually melanomas. Melanomas can be highly malignant in people, and in dogs, melanomas in the mouth and on the feet are usually very malignant. Oddly enough, melanomas on a dog's eye are usually, but not always, benign. They should be removed to be safe. It seems that I have seen a rash of eyelid problems in dogs lately.
Small tumors are common on eyelids.
A couple of weeks ago we removed a tiny eyelid tumor from Callie, a 9 year old Lhasa Apso. The lab reported that it was a low-grade malignancy, but completely excised. I think that is the first one I've seen that was not benign. Misty, a little black toy poodle, had much larger, angrier looking swelling that had been on her upper eyelid for a couple of weeks. We had to sedate her to get a small biopsy.