Tumor ??

[Jimmymueses]

Hey, everyone, I hope all is well I have this Feeder goldfish that has now grown rather large, I have noticed a large white bump on its dorsal fin, and it has become rather lethargic the last couple of days , so I wanted to know if anyone could help, I've attached some pictures below

 

[LyraGuppi]

Hello, welcome to TFF. c:
Do you know the water parameters of your tank? Things like Ammonia, Nitrite, and Nitrate. Those will help us greatly in finding the root of the problem.
It does look like a tumor. Is s/he showing any other symptoms besides the tumor and lethargy? Are there other fish in the tank?