A substance being studied in the treatment of cancer. It is made from an antibiotic called geldanamycin. Tanespimycin helps cause the breakdown of certain proteins in the cell, and may kill cancer cells. It is a type of antineoplastic antibiotic and a type of HSP90 inhibitor. Also called 17-AAG and 17-N-allylamino-17-demethoxygeldanamycin.