Bone marrow and thymus regeneration is a condition for thymoma development

Degeneration and regeneration of bone marrow was measured by nucleated cell number changes and of thymus and spleen by weight changes in adult female inbred SwisS mice given a single sub-lethal dose of methyl methanesulphonate (MMS), ethyl methanesulphonate (EMS), N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), or N-ethyl-N-nitrosourea (ENUA).Significant cell number decreases of the bone marrow were observed only following ENUA, the only one of the four agents capable of enhancing thymoma development in these mice. ENUA also caused the greatest significant weight decrease of the thymus and the spleen. Return to normal occurred before the 20th day of the experiment.It is suggested that bone marrow and thymus regeneration is an essential step in thymoma development.