TKT and lymphoma: In gene mutation tests in mammalian cells, benzene has been repeatedly observed to induce gene forward mutations in the L5178Y Tk+/− mouse lymphoma assay (MLA) (Oberly et al. 1985; Styles et al. 1985; Oglesby et al. 1989; Sofuni et al. 1996; Mitchell et al. 1997; Kirkland et al. 2005, 2011).