ETS transcription factor ESE-1/Elf3 is an independent prognostic factor of survival in HR+HER2+ breast cancer patients.

PURPOSE: The ETS transcription factor ESE-1 has been shown to be important in HER2+ breast cancer and ESE-1 mRNA expression has been shown to associate with prognostic outcomes in the HER2+ subtype, as well as in ER+, HER2+ luminal B patients. However, the clinical significance of ESE-1 protein expression remains unknown. The purpose of the current exploratory study is to evaluate the prognostic value of ESE-1 protein expression in molecular breast cancer subtypes with special emphasis on hormone receptor positive HER2+(HR+ HER2+) and the HER2 positive (HER2+-only) breast cancer patients. METHODS: We developed a mouse monoclonal anti-ESE-1 antibody, verified its specificity, epitope, and used immunohistochemical staining to assess ESE-1 expression in an IBC approved archive of 957 breast tumor samples. Using Pearson product correlation, contingency analysis, and long rank P value testing, we analyzed the association of ESE-1 expression with clinicopathological features and survival outcomes in HR+HER2-; HR+HER2+; HR- HER2- (Triple negative) and HR-HER2+ (HER2 subtype) patients. RESULTS: ESE-1, nuclear or cytoplasmic, was not significantly associated with survival outcomes in HR+HER2-, triple-negative, or HER2+-only breast cancer patients. However, high nuclear ESE-1 was associated with poor survival outcomes in hormone receptor positive (ERα+, PR+) HER2+ patients and was an independent prognostic marker for that group. CONCLUSIONS: This study provides evidence for prognostic significance of nuclear ESE-1 in ERalpha positive breast cancers patients also positive for HER2 indicating that crosstalk between ERalpha and ESE-1 in HER2+ tumors could be important for prognostic outcomes. Further studies regarding the nature of interaction between ESE-1 and ERalpha in these tumors are warranted.