Tc99m-sestamibi is a radiopharmaceutical that is taken up by cells with a high concentration of mitochondria, i.e. highly cellular/metabolically active tissues such as the heart but also abnormal tissues such as oxyphil cell parathyroid adenomas, myeloma and breast cancer (the basis of so-called scintimammography). This latter technique has a high specificity for cancer but uses significant radiation dose. In this case, a scan for hyperparathyroidism has shown up a breast cancer with metastases (also accumulating sestamibi) explaining the hypercalcemia.