Help My Goldfish w/a Tumour(?!) Please!!

[Irishgrl1982]

I have a 55 gallon freshwater tank which houses 2 goldfish I bought from a pet store "feeder goldfish tank" about 15 years ago. They surprised me and grew to large 11inch, Koi like, fish. About 2 years ago, one acquired a small bump on his right gill. I assumed it was bacterial or fungal, concerned it was contagious, so treated the tank with a variety of meds. I used natural cures like Melafix & PimaFix and then moved onto Erythromycin, General Cure, API Fungus Cure, Furan 2, Fin & Body Cure...pretty much everything; of which none worked. I couldn't find answers online(at that point I didn't think it may be a tumor!), my small town doesn't offer a "fish vet", and the bump didn't seem to bother him or grow much, so I continued to manage the tank like normal and keep a close eye on it. **sidebar: I try for water changes every other week(I can't physically do it more often), and use Seachem SAFE, Kent R/O Right, StressZyme+, QuickStart, & Tap Water Conditioner during each change.
Nothing changed much until last week when the bump literally seemed to "explode"/ become giant in size/changed color & is now making him act a bit sick. He still swims, eats, defecates, and doesn't rub or scratch at it. I am VERY UPSET & WORRIED & at a loss as to what to do. I've read some articles about iodine, peroxide treatment or even rubbing Neosporin on it, but am nervous. ANY & ALL HELP IS GREATLY APPRECIATED!!!

[Delapool]

No treatment known except maybe surgery that I know of (sounds like you have tried everything). Any clue on why it suddenly grew so quick?

[King Fisher]

It might be worth a shot to remove him from the tank wrapped with a wet cloth and remove the tumor with an x-acto knife. Place him in quarantine and treat the wound as you would a normal wound. I would go to this extreme due to it's size and it's potential to grow into his eye and cause him to be blind.

[Autumnsky]

I just read about a gill tumor which is caused by a thyroid problem, looks a bit similar. and can be treated in iodine water.
https://www.petmd.com/fish/condition..._Tumors?page=2