The bZIP class of transcription factors is one of the largest and includes numerous subfamilies such as the aforementioned CREB/ATF and C/EBPs, as well as activator protein-1 (AP-1), the musculoaponeurotic fibrosarcoma family and the nuclear factor (erythroid 2)-like (NFE2) or Cap‘n’collar (CNC) subfamily. The gene discussed is FOS; the disease is fibrosarcoma.