Etoposide induces an irreversible blockade of cells in the premitotic phases of cell cycle leading to accumulation of cells in the late S or G2 phase. Although its precise mechanism of action is not clear, cytotoxic effect appears to result from single and double strand breaks in DNA and DNA protein cross-links. Etoposide exerts its cytotoxic effect by interfering with the scission-reunion reaction of the enzyme topoisomerase II. The enzyme then covalently binds to DNA forming single strand, protein associated breaks. Etoposide also inhibits the transport of nucleosides across the plasma membrane. Hence it exerts its cytotoxic effect by interfering with DNA synthesis and repair.