I had WLE & radiotherapy (40Gy in 15#) last year for a 5 mm grade 1 IDC -margins clear, 0/1 lymph node, ER8, HER2 -. I have asymmetry, rib pain & swelling & saw my surgeon for a review. Ultrasound shows inflammation, course calcification with a vessel in one quadrant & possible post-radiotherapy costochondritis but no discrete lesions in the sternum. I've been referred for a full body bone scan, to correlate with a CT. I have severe arthritis. Why is it necessary to scan for metastasis?