FOS (Fos proto-oncogene, AP-1 transcription factor subunit) and JUN (Jun proto-oncogene, AP-1 transcription factor subunit) genes are proto-oncogenes that encode the transcription factor of activator protein-1 (AP-1), protein complex that is a major component in the MAPK signaling pathway [29] and are associated with the development of various tumor types. The gene discussed is FOS; the disease is neoplasm.