Abstract 4926: Loss of deiodinase type 3 expression distinguishes patients with poor prognosis in breast cancer

Background: Breast cancer is a highly heterogeneous disease and the identification of biomarkers that predict tumor biological behavior is warranted in improving patient survival. Thyroid hormones (THs) are critical regulators of cellular processes, and TH status alterations are known to contribute to cancer progression through all the hallmarks of cancer. Clinical studies associate THs levels with breast cancer mortality, and THs have been shown to influence breast cancer proliferation, apoptosis, and migration in in vitro models. Type 3 deiodinase (DIO3) is the main enzyme responsible for TH inactivation and disturbed DIO3 expression has been demonstrated in several human neoplasias. Here, we aimed to evaluate expression patterns and the prognostic significance of DIO3 in breast cancer.

Methods: The expression of DIO3 was assessed by immunohistochemistry in a primary cohort of 53 samples of breast tissue and was validated in a second cohort using the RNA-Seq data from TCGA database (BRCA study). We assessed DIO3 expression in both populations according to retrieved clinicopathological information. For methylation analysis, DNA methylation data from the TCGA-BRCA study were obtained. Regulation of DIO3 gene was investigated in MCF-7 and MDA-MB-231 cell lines.

Results: DIO3 expression was present in normal and tumoral breast glandular tissue. DIO3 mRNA expression was found to be reduced in tumor samples when compared to normal tissue (p<0.0001). Unexpectedly, loss of DIO3 expression was associated with increased mortality (HR 4.29; 95% CI 1.24-14.7) in the primary cohort. We then validated this finding in the secondary cohort. Patients with low DIO3 expression exhibited reduced overall survival (OS) when compared to those higher levels of DIO3 expression. Five-year OS rates were 90.4% and 77.4% in the high and low expression groups, respectively (p=0.0002). Among patients with metastasis, five-year OS rate was 70% in the high DIO3 group and 0% in the low DIO3 group (p=0.038). Additional experiments were performed to determine DIO3 regulation in breast cancer. In MCF-7 and MDA-MD-231 cells, DIO3 was subject to T3 stimulation and was under the regulation of MAPK pathway, as MAPK inhibition resulted in a 50% reduction of DIO3 expression (p=0.004). Methylation analysis revealed that DIO3 gene promoter is hypermethylated in tumoral cells when compared to normal tissue (p <0.0001).

Conclusions: DIO3 is expressed in normal and tumoral breast tissue. Here, we demonstrate a role for DIO3 as a prognostic marker in breast cancer, as loss of DIO3 expression distinguishes breast cancer patients with poor overall survival. Moreover, our fındings suggest the utility of DIO3 expression for stratifıcation of patients with metastasis. The finding that DIO3 gene is regulated by the MAPK pathway and that gene promoter is hypermethylated in breast cancer might have therapeutic implications.

Citation Format: Iuri M. Goemann, Vicente R. Marczyk, Mariana Recamonde-Mendoza, Marcia S. Graudenz, Simone M. Wajner, Ana Luiza Maia. Loss of deiodinase type 3 expression distinguishes patients with poor prognosis in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4926.