EGFR expression is associated with decreased benefit from trastuzumab in the NCCTG N9831 (Alliance) trial

The subject invention provides a method for treating a patient having a tumor associated with HER2+ breast cancer comprising: measuring in a sample of the patient's tumor a level of expression of epidermal growth factor receptor protein by using an antibody that detects the cytoplasmic domain of epidermal growth factor receptor; and comparing the level of expression of epidermal growth factor receptor protein in the patient's tumor so measured with a reference value; wherein if the level of expression of epidermal growth factor receptor measured is higher than the reference value, treating the patient with a therapy other than trastuzumab.