Large mass in between the ring finger and pinky? (i've deiced to ask this question outside the dermatology area just in case, boarding the range for the question as it where). I think it started out as some type of callus a few years ago, just from getti

Unless you have. something that rests in that area regularly , a callus is unlikely. I would get into dermatologist to get biopsy to be sure ( it could be a wart or many other things). hOpe that helps.
It . It could be a ganglion, an inclusion cyst, or fibroadenoma, and there are other possibilities as well. As it sounds quite large you should have it medically evaluated. If it becomes red, painful, or you have red streaks then you will need to be seen as an emergency.