Activator protein 1 (AP-1) protein dimers consist of multigene families of proteins and transcriptional factors consisting of the Fos proteins (c-Fos, v-Fos, Fos B, Fra-1, and Fra-2); Jun proteins (c-Jun, v- Jun, Jun B, and Jun D); activating transcription factors (ATF1-4, ATF6, B-ATF, and ATFx); and musculoaponeurotic fibrosarcoma (Maf) proteins (c-Maf, Maf B, Maf G/F/K, and Nrl) [19,20,21,22]. The gene discussed is JUNB; the disease is fibrosarcoma.