Abstract: A method for determining the likelihood that a therapy involving administration of tamoxifen to a patient afflicted with an estrogen receptor positive breast cancer will provide a therapeutic benefit to the patient which comprises determining the level of expression of epidermal growth factor receptor present within a non-nuclear compartment in cells present in a breast tissue sample from the patient; and comparing the level of expression so obtained to a predetermined level of expression wherein the likelihood the therapy will provide a therapeutic benefit to the patient is greater if the level of expression in step a) is less than the predetermined level of expression.