Correlations of estrogen receptor (ER) related genomic transcription and ER gene expression with increasing AJCC stage of ER-positive breast cancer

Abstract

1044 Background: Advanced stages of ER-positive breast cancer may have decreased tumor dependence on estrogen, possibly due to biological selection and/or progression. The sensitivity to endocrine therapy (SET) index measures transcriptional activity of the ER genomic pathway (165 ER-related genes). We investigated whether expression of genes for receptors ER (ESR1), progesterone receptor (PGR), or HER-2 (ERBB2), the SET index, or a housekeeper gene (GAPDH) vary by stage of ER-positive breast cancer. Methods: We evaluated gene expression profiles (Affymetrix U133 microarrays, Affymetrix, Santa Clara, CA) from 956 patients’ clinical samples of ER-positive breast cancer, including 290 new samples profiled at MDACC and 666 samples from published datasets. Microarray data were uniformly normalized, log-transformed, and expression levels for single genes and the SET index were compared to pathologic AJCC stage (315 patients were stage I, 362 stage IIA, 151 stage IIB, 29 stage III, 27 stage IV at initial presentation, and 72 stage IV previously treated and/or at relapse) using a median ordered regression analysis (p < 0.05 was significant). Results: SET index significantly decreased with advancing pathologic stage (p < 0.001), and PGR expression levels showed a similar, but lesser, effect (p = 0.014). However, expression levels of ESR1 and ERBB2 did not vary by stage. Overall, GAPDH gene expression increased with stage (p < 0.001), but that effect was only observed in stages III and IV. Expression of these genes was not significantly different between stage IV disease at initial presentation or at relapse. Conclusions: Expression levels of ESR1 and ERBB2 receptor genes did not vary, but ER-related genomic transcription (SET index and, to a lesser extent, PGR) declined significantly with increasing pathologic stage. This suggests that ER-positive breast cancer tends to have less transcriptional dependence on estrogen with increasing pathologic stage. The observed increase in expression of GAPDH in stages III and IV might reflect higher metabolic activity in advanced ER-positive breast cancer and deserves further study. [Table: see text]