A phosphate salt of a semisynthetic derivative of podophyllotoxin. Etoposide binds to the enzyme topoisomerase II, inducing double-strand DNA breaks, inhibiting DNA repair, and resulting in decreased DNA synthesis and tumor cell proliferation. Cells in the S and G2 phases of the cell cycle are most sensitive to this agent. OR A drug used to treat testicular and small cell lung cancers. It is also being studied in the treatment of several other types of cancer. Etoposide phosphate blocks certain enzymes needed for cell division and DNA repair, and it may kill cancer cells. It is a type of podophyllotoxin derivative and a type of topoisomerase inhibitor. Also called Etopophos.