Hi Gem8. Welcome to the forum.

We're not doctors here, so we can't diagnose your lump, but the take home message is that most lumps are harmless. There are numerous possible reasons for lumps, and cancer is way down near the end of the list.

Your doctor is doing the right thing in sending you for an MRI, and don't be too surprised if you're referred to a specialist and/or the lump is biopsied. Don't be alarmed if you're sent for an "urgent" referral for "suspected cancer".  Many people are similarly referred each year, and nine out of ten turn out not to have cancer.  I myself have been "urgently" referred for suspected cancer on two occasions in the last 3 years, and each time nothing nasty has been found - although I did need to have endoscopies and an MRI! 

Right now, you have no reason to suspect that this is cancer. Right now it's an unidentified lump which may well turn out to be a cyst or a lipoma or something else equally harmless. You might need surgery to remove it, or it might resolve on its own, but there is no undue reason to be alarmed. 

So please try to keep calm, and don't panic.

PS. Don't bother asking the MRI radiographer whether the images show anything nasty. They're not allowed to tell you because they're not qualified to interpret what they see. The images need to be examined and interpreted by an experienced radiologist (a qualified doctor) who will write a report and send it back to the doctor who ordered the scan. 

PPS. If you've never had an MRI before, my advice is to take a favourite CD which contains a lot of short familiar tracks which will help you pass the time(you probably won't be able to take an iPod because the MRI's magnetic fields could well damage it).  Ask the radiographer to turn the machine's internal fan onto maximum because the scans may make you feel warm, and to count down the number of scans left to go after each one finishes. A single scan lasts about 4 minutes, and the machine makes so much noise that you're given headphones. If you can't hear your CD, ask for the volume to be increased slightly. You'll probably want to keep your eyes closed as much as possible during the procedure. It's not much fun, but it is necessary.