What Is This Lump On My New Black Phantom?

[KCB]

I've had her since Friday and she is currently in quarantine, I've only just noticed it today though I'm not sure whether she always had it. It's a brownish looking lump on her right side by the pectoral fin. She's showing no other sign of illness and there's been no aggression between the other fish that I've noticed.
 

 
 
I hope it's not serious 

 

[KCB]

Bump. Any guesses?

 

[DoubleDutch]

Looks like a tumor to me.

 

[KCB]

Thank you for the response. I thought that could be the case but I've also heard about fish 'zits' as well so was hoping it wasn't a tumor. I'll just have to keep an eye on her I guess and put her to sleep if it becomes an issue.