A substance being studied in the treatment of cancer. It is made from an antibiotic called geldanamycin. 17-AAG 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-N-allylamino-17-demethoxygeldanamycin and tanespimycin.