Ask your Doctor for a PET scan. If the lump is cancerous it will show on the scan. Lumps as small as 2mm. are found on PET scan. It is an expensive test, state of the art, and your insurance may fight it due to the cost, but is better than mamogram or ultrasound. Best of luck to you.
Dear lisamw, Different types of tests help to give different information. A mammogram is an x-ray of the breast tissue, an ultrasound is use of sound waves to differentiate between solid or fluid filled tissue. A finding that may be seen on a mammogram is not always seen on an ultrasound. The findings from both the mammogram as well as ultrasound will be considered by the surgeon and they will use that information as well as physical exam to determine the recommendation for the next step in evaluation.