I have an intermittent throbbing pain behind my breastbone and a general aching there when I am still. I am a 55 year old female, weighing 134 lbs., with a medical history of metastatic breast cancer with spread to the bones. Last scans showed no sternum involvement and I am wondering why it throbs when I move - ie. stand up, sit, turn suddenly. Painful to roll over in bed, particularly on to right side.