PROS1 and neoplasm: Several factors may have an influence in diminished 99mTc-MIBI uptake in the tumor: Poor vascularization and accessibility of 99mTc-MIBI to the tumor, early stage of apoptosis, decreased viability and electrical gradients in “over-aged” and hypoxic cells, multidrug resistance proteins and/or over expression of the anti-apoptotic protein Bcl-2, preventing any mitochondrial accumulation (23).