Cyclophosphamide induces osteopetrosis in rats

The effect of a single oral dose of cyclophosphamide in six-week old random outbred albino rats on hematologic, immunologic, and pathologic parameters was studied. As expected, doses that decreased the number of circulating lymphocytes and suppressed the blastogenic response to Concanavalin A, a T cell mitogen, also caused extramedullary hematopoiesis in the liver and spleen and depletion of cortical lymphocytes in lymph nodes. However, a novel histomorphologic finding of this study was osteopetrosis. It would appear that cyclophosphamide interferes with a subpopulation of lymphoid cells that are involved in the formation of osteoclastic cells.