Just like humans, fish get tumors, and at 5 years of age (maybe equivalent to 50 or more in humans) a distinct possibility.
I use a veterinary text book called Self-Assessment Color Review of Ornamental Fish, by Gregory Lewbart, published by the Iowa State University Press, before adding any medications.
This text book is full of case studies, and color photos, and X-ray plates. There are at least 10 studies having to do with tumors (granulomas the term in the text book) in ornamental fish, so not uncommon.
Medication would of little use in these situations, unless to prevent infection after surgery.