The chloride salt of a radioactive isotope of strontium. Strontium chloride Sr 89 is taken up and incorporated preferentially in metastatic lesions in bone where it emits cytotoxic beta radiation, resulting in an inhibition and/or reduction of tumor growth and so tumor-related bone pain. or A salt form of the radioactive metal strontium-89 that is absorbed by a part of growing bone. It is being studied in the treatment of bone pain caused by cancer that has spread to the bone.