This could mean that your hamster is sick. You should bring it to the vet as soon as possible to ensure that no infections are present. It could be a natural deformity that will do no damage, but it is best to make sure.
Same with my hamster but I think he was born like that. It's just a little bigger in size but I never noticed until today! I may be okay because sometimes things that are the same size put beside each other makes one look bigger and the other look smaller.