I Had A Bilateral Mastectomy 8 Years Ago. Had Chemo.

I had a bilateral mastectomy 8 years ago. Had chemo. Went 7 years Cancer free. Two years ago the Cancer returned to my bones. Have been under treatment with monthly infusions of Zometta. Just noticing a pain in my right breast where the original Cancer was. The pain is sharp. Not constant. Not under ny arm but the pain is inside my breast. What could this be