Background and Objectives: We investigated whether expression levels of c-erbB-2 and p53 proteins in breast cancer tissues differ in primary and metastatic lesions. Methods: Immunohistochemical staining or sandwich enzyme immunoassay was used to determine expression levels of c-erbB-2 and p53 proteins in 42 breast cancer samples from 21 patients. Estrogen (ER) and progesterone receptors (PgR) were also measured by enzyme immunoassay in each case. All patients had undergone radical surgery for primary tumors and surgical resection of asynchronous metastatic lesions. Thirteen patients (62%) were premenopausal and 14 (67%) received postoperative adjuvant therapies. Median disease-free survival time was 26 months (range, 5-104). The resected metastatic lesions included 1 in the liver, 3 in the lung, and 3 in the supraclavicular lymph nodes. The remaining 14 were local skin lesions. Results: There was no difference in the positivity rate of c-erbB-2 (38%: 8/21) and p53 (39%: 7/18) expression between the primary tumors and the recurrent lesions. In addition, no discordant c-erbB-2 or p53 expression was observed between the primary tumors and their respective metastatic lesions. Positivity rates for ER and PgR were 50% (10/20) and 60% (12/20) for the primary tumors, but only 25% (5/20) and 30% (6/20) for the recurrent lesions, respectively (P โซืกโฌ 0.19 for ER and P โซืกโฌ 0.11 for PgR). Conclusions: c-erbB-2 and p53 expression levels in breast cancer cells were almost unchanged as the disease progressed and/or in response to adjuvant therapies, regardless of the hormone receptor status.