Major impact of sampling methodology on gene expression in estrogen receptor positive breast cancer

To investigate the impact of sampling methodology on gene expression data from primary estrogen receptor positive (ER+) breast cancer biopsies. Analysis of global gene-expression measured in core-cut biopsies at baseline and surgery from patients randomised to receive either 2-week’s presurgical aromatase inhibitor (AI, n=157) or no presurgical treatment (n=56) revealed genes most markedly altered in the AI group (e.g. FOS, DUSP1, RGS1, FOSB) were equally altered in the no-treatment group; some widely investigated genes that were apparently unaffected in the AI group (e.g. MYC) were counter-altered in the Control group masking actual AI-dependent changes. In the absence of a Control group these artefactual changes would likely lead to the most affected genes being the erroneous focus of research. The findings are likely relevant to all archival collections of ER+ breast cancer. Global gene-expression measured in core-cut biopsies at baseline and surgery from patients randomised to receive either 2-week’s presurgical aromatase inhibitor (AI, n=157) or no presurgical treatment (n=112).