Goldfish cancer?

Hello everyone,

I am new here and hoping to get some advice. I have various goldfish
in my tank but the one that it worrying me is a 4 year "common" fish,
which I call ginger. The problem now which I am not sure what to do.
Now she developed a bubble(protrusion) on outside of her body. Prior
to this, maybe a year ago, she was continuously getting darker color
in the same area where the big bump is sticking out.

Is this cancer? Is there anything I can do for her. I hope this will
go away on its own. I am very attached to this fish. Ginger does not
look like she is suffering now. I am hoping for the best for her.

Now how old do these fish get? She's not a comet but a big fat common
goldfish. She was never gold but a "ginger" color.

Thanks amy