Long term storage stable fulvestrant-containing compositions are disclosed. The compositions can include fulvestrant a solvent selected from dimethyl sulfoxide (DMSO), glycofurol, N-methyl pyrrolidone, and mixtures thereof an oil mixture selected from a mixture of caprylic and capric triglycerides, a mixture of caprylic, capric and linoleic triglycerides, a mixture of caprylic, capric and succinic triglycerides, and a mixture of propylene glycol dicaprylate and propylene glycol dicaprate and a sustained release member selected from benzyl benzoate, dihydrolipoic acid, benzyl alcohol and lipoic acid. The fulvestrant-containing compositions have less than about 5% total impurities, on a normalized peak area response (“PAR”) basis as determined by high performance liquid chromatography (“HPLC”) at a wavelength of 223 nm, after at least about 24 months of storage at a temperature of from about 5° C. to about 25° C.
