 Sunitinib, a type of tyrosine kinase inhibitor TKI has been approved by the FDA as a standard of care treatment for renal cell carcinoma RCC. Fatigue is a very common side effect of sunitinib that frequently causes dose reductions. The cause of this fatigue remains unclear. It has been shown that TKIs disrupt growth factor pathways in muscles leading to muscle shrinkage. If sunitinib associated fatigue is due to altered muscle physiology at a molecular level, there will be observable changes in the uptake of 99mTc-sestamibi in scintigraphy scans. The study objective is to determine if sunitinib-induced fatigue as determined by VO2 and QOL fatigue related questionnaire responses are correlated to molecular changes in the muscles as evidenced by 99mTc-sestamibi uptake. 