Check with a specialist about the tumour. Is it definitely contained in the toe? If it's spread I wouldn't have it cut into as I feel that this can set off increased growth. As to having a toe removed, one of my bitches had a toe on her front foot removed because it was badly damaged. The vet said that she would always limp but she was back in the show ring after the operation and not one judge she went under noticed the missing toe! She moved as perfectly as ever.