Not necessarily. However, it should be removed or atleast biopsied. They remove polyps in the colon for fear that they might turn cancerous, so I'd think the same would apply gynecologically as well.
No, most polyps are not cancerous, but you normally have them removed. I had a fairly large one last March and it was a very simple surgery--didn't have to stay overnight--and I felt instantly better the next day. No more bleeding. Took one day off work and went right back.
Take care!!