"Shadow" in left breast mammogram

I had breast cancer (stage 2 - invasive; 3 lymph nodes affected) in my right breast, had a mastectomy in Jan. 2008., chemo, etc... and things have been getting back to normal until I recently felt a lump in my left breast.  I went for a recommended mammogram of the left breast and they found nothing where I felt the lump but said they do see a shadow in all views from the top/side that was not there in my mammogram 6 months ago - they have advised me to see my surgeon.  I am a "fact" junkie - and am frustrated waiting the 12 days to see the surgeon.  What could this be?  Is it possible that it is NOT cancer?  

[japdip]

It could certainly be something OTHER than cancer. I think it very natural to think the worst ... especially if you've been "there" before. I'm surprised that they didn't do an Ultrasound following the Mammogram which may have presented a different picture and possibly more information. Wish I could say more to reassure you but as you well know that's impossible until you get that "benign" report. Hang in there and stay busy; hoping the time flies until you see the Surgeon.   Kindest regards ....

[daugenst]

They did also do an ultrasound - which I failed to mention.  Report came back bi-rads 4.  My mastectomy began with a bi-rads 4 report as well so I'm not feeling very optimistic.  I have a work conference all week and another client visit next week so can't help but stay busy.  Thanks so much for your response - it means a lot to me!