A substance being studied as a way to find cancer in the body. It is also used to find sentinel lymph nodes in breast cancer. It contains a radioactive substance called technetium linked to a substance called sulfur colloid. Sulfer colloid is taken up by special cells in lymph tissue, and in the liver, spleen, and bone marrow after it is injected. A machine or probe that detects radioactivity is used to find where the Tc 99m sulfur colloid is in the body. It is a type of radiopharmaceutical and a type of radioimaging agent. Also called Tc-99m SC and technetium Tc 99m sulfur colloid.