A semisynthetic derivative of podophyllotoxin that exhibits antitumor activity. etoposide inhibits dna synthesis by forming a complex with topoisomerase II and dna. This complex induces breaks in double stranded dna and prevents repair by topoisomerase II binding. Accumulated breaks in dna prevent entry into the mitotic phase of cell division, and lead to cell death. etoposide acts primarily in the G2 and S phases of the cell cycle.