Cat,
get yourself to an ENT as soon as possible, and get a proper medical diagnosis. The only way to definitively determine if a lump is cancerous is through biopsy. Any lump in your mouth that lasts more than 2 weeks is worthy of concern.

The internet is a great resource for a lot of things, but it is NOT at all useful for diagnosing a disease, especially one as deadly as this.

Get to the Doctor, as soon as possible
Wayne