Lumps should never be an indication of cancer down below. The truth is we all get different types of bumps down there for many different reasons, and usually it's nothing to worry about.
Also, if it was cancer and its been there for 6 years, surely you'd of felt the effects of cancer. My guess is its nothing serious. But to ease your mind, see a doctor, they might be able to get rid of it. Don't be scared.
Check out pictures for a Bartholin's cyst and see if that matches your lump. If it does, you have nothing to worry about. Good luck.