It is unlikely that you would have had bone cancer (osteosarcoma) of the sternum for 5 years now without there being any visible or palpable mass. That being, said, as I am not able to examine you, you should ask your doctor to have a look at this area. If he/she identifies any abnormalities, then a bone scan or/and CT scan should be performed.
Sincerely,
Robert A. Wascher, MD, FACS
www.doctorwascher.com
Author, "A Cancer Prevention Guide for the Human Race"