Since the development of novel immunotherapy using Herceptin as the first agent specifically indicated for HER-2/neu overexpression in metastatic breast cancer, there has been interest in using HercepTest as a predictor of response to such therapy. There is debate whether it is justifiable to perform HercepTest on every newly diagnosed breast cancer, since only approximately 43% of the cases will have related metastatic disease, and Herceptin is indicated only for breast cancer with metastatic disease. It may be more cost-effective to limit HercepTest to the related metastatic lesions. Therefore, it is important to assess whether the pattern of HER-21neu overexpression of metastatic breast cancer is also present in the primary lesion. HercepTest was performed on formalin-fixed, paraffin-embedded tissue sections of 56 primary breast cancers and their corresponding metastatic lesions. The protocol and scoring guidelines recommended by the manufacturer were followed. Tissue sections (5 microm) of a primary and the metastatic lesion from the same case were placed parallel on a single glass slide. The pattern and intensity of HER-2/neu overexpression (32%) in the primary and metastatic lesions were found to be nearly identical. Heterogeneity was observed in only one case. The score of primary cancer was 3+, and the metastatic lesion was 2+. Both were reported as positive. Intratumor heterogeneity (1+ to 3+) was also noted in two (4%) cases. However, the same pattern was found in both the primary and related metastatic lesions. The nearly identical HercepTest results in the primary and metastatic lesions suggest the potentiality of limiting the HercepTest to breast cancer-related metastases. Currently, any superficial and most deep-seated metastatic lesions can be easily sampled by fine needle aspiration biopsy or core biopsy, providing adequate samples for HercepTest. Eliminating unnecessary use of the HercepTest may provide a cost-effective alternative approach to the management of breast cancer patients.