This invention provides methods for treating cancer, particularly hematopoietic tumors of lymphoid or myeloid lineage, prostate cancer, lung cancer, gastrointestinal stromal tumor, breast cancer and melanoma, which comprise administering to the mammal a compound, salt, hydrate, tautomer or N-oxide according to formula (I):and in particular, those of subgenus VIIaThese compounds inhibit or modulate the activity of the heat shock protein Hsp90.