Quantitative reverse transcription-polymerase chain reaction (RT-PCR) used to detect minor changes in specific mRNA concentrations may be associated with poor reproducibility. Stringent quality control is therefore essential at each step of the protocol, including the PCR procedure.We performed inter-laboratory quality control of quantitative PCR between two independent laboratories, using in-house RT-PCR assays on a series of hormone-related target genes in a retrospective consecutive series of 79 breast tumors. Total RNA was reverse transcribed in a single center. Calibration curves were performed for five target genes (estrogen receptor (ER)a, ERb, progesterone receptor (PR), CYP19 (aromatase) and Ki 67) and for two reference genes (human acidic ribosomal phosphoprotein PO (RPLPO) and TATA box-binding protein (TBP)). Amplification efficiencies of the calibrator were determined for each run and used to calculate mRNA expression. Correlation coefficients were evaluated for each target and each reference gene.A good correlation was observed for all target and reference genes in both centers using their own protocols and kits ðP < 0:0001Þ. The correlation coefficients ranged from 0.90 to 0.98 for the various target genes in the two centers. A good correlation was observed between the level of expression of the ERa and the PR transcripts ðP < 0:001Þ. A weak inverse correlation was observed in both centers between ERa and ERb levels, but only when TBP was the reference gene. No other correlation was observed with other parameters.Real-time PCR assays allow convenient quantification of target mRNA transcripts and quantification of target-derived nucleic acids in clinical specimens. This study addresses the importance of interlaboratory quality controls for the use of a panel of real-time PCR assays devoted to clinical samples and protocols and to ensure their appropriate accuracy. This can also facilitate exchanges and multicenter comparison of data.

The cell type heterogeneity within clinical cancer tissue samples may affect the accuracy of gene expression analysis. In order to validate our laser microdissection (LMD) method using the Leica AS LMD system (LEICA Microsystems), we compared the mRNA levels of three major genes involved in breast cancer (ERalpha, PR, HER2), measured by means of real-time quantitative RT-PCR, in 5000 microdissected malignant epithelial cells and in corresponding bulk tumor homogenates from 14 patients. We also compared the mRNA level results to protein expression measured by immunohistochemistry (IHC) on the same tumors. For the three genes, significant correlations were found between mRNA results obtained on microdissected cells and IHC. Comparison between IHC and mRNA results obtained on microdissected cells and bulk tumors showed that in all cases microdissection enhanced the sensitivity of assessing target gene transcript levels and was essential for their accurate evaluation in heterogeneous tumors.