Hi Lollypop.
In the past I have always advised going straight to biopsy to make certain - and actually went that route myself. But in more recent days as I've continued to research diagnosis and treatment, I've come to question that "wisdom."
Certainly, biopsy is the only "sure" way to know if cells are cancer (and even then it's not fool-proof), but biopsy in itself may present a risk that scientists and drs have been loath to consider: specifically the possibility of taking a well-contained cancer and seeding it to other tissues.
So, maybe consider taking the middle ground. If you have the insurance coverage, get the MRI done first. That will show you if there is a really compelling reason for biopsy - if not, then you've saved yourself some pain. If biopsy is indicated from the MRI, you would only have a matter of several weeks delay at the most.
Go with your gut feelings - do what you need to do to take prudent action while at the same time trying to minimize risk.
Sincerely,
Tre