abnormality in mammography

Just had my annual mammogram and for the first time (I'm 52 YO) got a call that there was an abnormality in one of the images.  Apparently, it didn't show in the other image of that breast.  Unfortunately, this hospital doesn't have my las 5 years of results because those were done elsewhere.  They are waiting for those images to be delivered for comparison but they have noted that his abnormality did not appear on the last records they have which are from 2005.  Obviously, I'm concerned and the waiting is difficult.  What can you tell me about the fact that this abnormality doesn't appear in both images of that breast?  Thanks.

[Cleveland Clinic]

Dear professionalworrier,  Over the internet without seeing the scans for comparison of images etc. it is impossible to give an explanation for the findings.  You will need to discuss your question with your doctor or the radiologist.