Using a quantitative real-time RT-PCR technique we have compared the expression of a number of genes in two different human breast cancer model systems for development of acquired resistance to antiestrogens. The model system developed at the Danish Cancer Society comprises the cell lines MCF-7, MCF-7/TAMR-1, MCF-7/182R-6 and MCF-7/182R-7, and the model system developed at the Lombardi Cancer Research Center consists of the cell lines MCF-7/LCC1, MCF-7/LCC2 and MCF-7/LCC9. The findings on the well-known parameters estrogen receptor (ER)alpha, progesterone receptor (PR) and epidermal growth factor receptor (EGFR) are in good agreement with previous reports, thus documenting the usefulness of the real-time RT-PCR technique for multiparametric RNA analysis. The gene expression levels in the two model systems were found to be quite similar in relation to ERalpha, AIB1 (amplified in breast cancer-1), breast cancer antiestrogen resistance gene 1 (BCAR1) and ErbB-2 mRNA expression, whereas significant differences were observed on the expression of ERbeta, multidrug resistance gene 1 (MDR1), PR and EGFR. Furthermore, the presented data suggest that ERbeta, AIB1, BCAR1, CYP19 and MDR1 are unlikely to be causally involved in development of antiestrogen resistance in these breast cancer cell lines.

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