Lenalidomide is a derivative of thalidomide. In vitro, lenalidomide has three main activities: direct anti-tumor effect, inhibition of the micro environment support for tumor cells, and immunomodulatory role. It induces tumor cell apoptosis directly and indirectly by inhibition of bone marrow stromal cell support, by anti-angiogenic and anti-osteoclastogenic effects, and by immunomodulatory activity.