PET Imaging With Tc-94m Sestamibi to Assess Resistance to Chemotherapy

Background: * Tc-94m sestamibi is a radioactive imaging drug approved by the Food and Drug Administration to help photograph and study bodily functions. * Tc-94m sestamibi accumulates in tumor cells and is eliminated from them in much the same way that some chemotherapy drugs are eliminated from cancer cells in patients with drug resistance. * P-glycoprotein is a protein found on the surface of some cancer cells. The protein causes the cells to pump out, or reject, some types of chemotherapy drugs. P-glycoprotein also makes the cells reject sestamibi. * Some drugs, including a drug called tariquidar, may block the pumping action of P-glycoprotein, giving the chemotherapy more time to work. Tariquidar can also help sestamibi stay in the cells longer. Objectives: -To evaluate the use of sestamibi for determining if chemotherapy is being rejected and if enough of the blocking drugs are present to stop the rejection. Eligibility: -Patients18 years of age and older with a tumor 2 cm or larger who are enrolled in or are eligible for enrollment in an active National Cancer Institute treatment protocol. Design: * Patients have two scans, one before receiving any drugs and a second 1-2 hours after receiving tariquidar. The second scan is done 72 or more hours after the first. For both scans, Tc-94m sestamibi is injected into a vein and a series of pictures are taken with an imaging camera called a PET (positron emission tomography) scanner. The pictures show where the sestamibi distributes in the body and monitors the effects of tariquidar on drug resistance. Blood samples are collected during the scan to examine the effect of tariquidar on P-glycoprotein in normal cells. * Some patients may be asked to undergo a tumor biopsy to test for the presence of the P-glycoprotein on their cancer cells. This will be requested only in patients whose tumor is easily accessible and in whom a biopsy can be done with minimal risk.