Signal transducer and activator of transcription 3 (STAT3) is a protein that can be activated by certain signals in the body. When it is constantly active, it can contribute to the development of different types of blood cancers. These cancers can grow, spread, and avoid cell death more easily. Scientists are studying how to block the activity of STAT3 to potentially treat these blood cancers like leukemia, lymphoma, and myeloma.