Estrogen receptor alpha (ERα) mRNA copy numbers in immunohistochemically ERα-positive-, and negative breast cancer tissues

BACKGROUND: The presence of ERα is the basis for treating breast cancer patients with targeted molecular therapies that block estrogen stimulation of breast cancer cell division. To select patients for the above therapies, currently, the ERα presence in breast cancer tissues is determined in clinical laboratories by microscopically scoring the slides subjected to immunohistochemistry (IHC). This method is not quantitative, highly subjective and requires large amount of tumor tissue, therefore, cannot be applied to sterotactic and ultrasound guided biopsy samples. To circumvent these problems, we previously developed quantitative real-time PCR based molecular assay that can be applied to determine mRNA copies of ERα in picogram amounts of total RNA from tumor samples. However, it is not known how the mRNA copy numbers correlate to IHC positive and negative status. METHODS: In the current study we determined the copy numbers of ERα mRNA by Q RTPCR in breast cancer tissues that were graded as ERα-positive and negative by 1) IHC and 2) functional estrogen binding assay and statistically analyzed the data. RESULTS: We demonstrate here that ERα mRNA copy numbers are not significantly different in tissues that are graded as positive by IHC and ligand binding assays. We establish here a cut of value of 5 × 10(6 )copies per 10(10 )mRNA copies of GAPDH with an Odds Radio of 39.4, Sensitivity of 0.81 and Specificity of 0.90 in breast cancer tissues that are negative for ERα protein by IHC and estrogen binding assays. ROC analysis of the data gave an area of 0.8967 under the curve. CONCLUSION: We expect that the cut off values determined here will be highly significant for applying molecular assay in the place of IHC in clinical laboratories for evaluating the presence of ERα for prognostic and therapeutic purposes.