Detection of sentinel nodes with radiopharmaceuticals

Sentinel lymph nodes have been found to be an indicator of lymph node metastasis in breast cancer. In Japan, the theory and concept of sentinel lymph nodes in breast cancer have begun to be applied to carcinomas of the digestive system. Based on clinical experience in the detection of sentinel lymph nodes with radiopharmaceuticals, differences and similarities between the radiopharmaceuticals, methods, and techniques used to detect sentinel lymph nodes have been assessed in relation to breast cancer and carcinomas of the digestive system (including carcinomas of the esophagus and large intestine). The greatest difference between the methods used for breast and digestive cancers is the site of administration of the radiopharmaceutical. In breast cancer, the radiopharmaceutical is administered into a superficial organ (i.e., the mammary gland), whereas in carcinomas of the digestive system, it is administered into a deep organ (i.e., digestive tract). Another obvious difference is in lymph flow, i.e., the flow of the mammary glands is subcutaneous whereas lymph flow in the digestive tract is submucosal. Two radionuclide diagnostic methods are available to detect sentinel lymph nodes: sentinel lymphoscintigraphy with a gamma camera and a method that involves the use of a gamma probe intraoperatively. Radiopharmaceuticals used to detect sentinel lymph nodes must be smoothly transferred from the site of administration into the lymph, and uptake by the sentinel lymph node must continue for a long time without excessive flowing to lower reaches. The optimal particle size remains a matter of controversy, and no radiopharmaceuticals appropriate for lymphoscintigraphy have ever been approved in Japan. The authors compared the pharmacokinetics of three different radiopharmaceuticals used for sentinel lymphoscintigraphy in breast cancer (99mTc-labeled albumin, 99mTc-labeled tin colloid, and 99mTc-labeled phytic acid) and founded that the detection rate was lowest with phytic acid, followed by albumin, and then tin colloid. Although the authors mainly use 99mTc labeled phytic acid for carcinomas of the digestive system, there is a report suggesting a higher detection rate with 99mTc labeled tin colloid. Thus, the rate of detection sentinel nodes of carcinoma of the digestive system with 99mTc labeled phytic acid might be equivalent to the rate with of 99mTc labeled tin colloid. It is therefore considered necessary to choose the most appropriate radiopharmaceutical for detection of sentinel lymph nodes according to the organ or tissue that is the site of the cancer. Although the detection rate by scintigraphy is lower in breast cancer than with the gamma probe, scintigraphy should also be performed in breast cancer, because useful information is obtained for surgery. Preoperative scintigraphy is indispensable in carcinoma of the digestive system because the gamma probe is difficult to use without the results of scintigraphy. Earlier detection of sentinel lymph nodes can be expected by combined use of a gamma probe and scintigraphy. (K.H.)