None of the 18 pretreatment samples from patients who responded to therapy expressed c-erbB2, and 1 of 18 expressed EGFR, Of the nonresponders, 7 of 18 expressed EGFR pretreatment, and 4 of 18 expressed c-erbB2 (1 patient expressed both receptors), Results confirmed previous findings that when considered independently, expression of either receptor pretreatment tended to predict for a poor chance of response (EGFR, P = 0.046; c-erbB2, P = 0.11), Importantly, patients who were either EGFR positive and/or c-erbB2 positive had a much poorer chance of response than ''double negatives'' (response rates of 1 of 11 and 17 of 25, respectively; P = 0.0039),

At the time of disease progression compared to pretreatment, there was no significant change in expression of either receptor, irrespective of initial response, The inverse relationship between EGFR and estrogen receptor was maintained at relapse on tamoxifen, These data argue strongly against the acquired expression of these receptors during treatment playing a major role in the development of tamoxifen resistance in human breast cancer.