Abstract B58: Claudin-2 is an independent negative prognostic factor in breast cancer and specifically predicts early liver recurrences
Authors: Kimbung Siker , Fernö Mårten , Malmström Per , Hatschek Thomas , Hedenfalk Ingrid 
Published: August 2014

Background: The liver is the third most frequent breast cancer metastatic site and hepatic metastases confer an inferior prognosis relative to bone and lung metastases. Metastatic sites differ depending on the phenotype of the primary tumor, but the mechanisms driving this organ-specific tropism are not well understood. The scarcity of clinical samples from liver metastases has greatly impeded the development of a human liver metastasis gene signature for predicting the likelihood of liver metastasis after adjuvant therapy and identifying biomarkers for liver-specific recurrence from breast cancer.

Objectives: This study was designed to provide a description of the transcriptional landscape of breast cancer site-specific metastases and to investigate the role of claudin-2 (CLDN2) expression in breast cancer progression and prediction of liver recurrences.

Methods: Global transcriptional profiling of breast cancer metastatic lesions (n=92) from different anatomical sites was performed and genes differentially expressed between liver metastases versus other metastatic sites were identified. Immunohistochemical (IHC) staining of CLDN2 protein was performed on tissue microarrays of primary tumors and matched lymph node metastases present at the time of primary diagnosis in a cohort of patients with metastatic disease (n=192), and was validated in an independent cohort of node-negative breast cancer patients (n=208).

Results: Unsupervised principal component analyses and hierarchical clustering showed that the previously described and well-known intrinsic subtypes constituted the strongest discriminator between the metastatic lesions, and in addition revealed that liver metastases displayed a unique gene expression profile. Gene ontology analyses of genes significantly altered in the liver compared to other sites revealed a down-regulation of extracellular matrix remodeling, tight-junctions and focal adhesion genes in the liver. Remarkably, however, CLDN2 (a tight-junction family member) was found to be up-regulated in the liver metastases (P&lt;0.001). IHC staining for CLDN2 in primary tumors and matched lymph node metastases revealed that it was more frequently expressed in lymph node metastases compared to primary tumors (P=0.001). Also, consistent with mRNA expression levels, high protein expression was more frequently observed in tumors from patients who eventually developed a liver metastasis (p=0.02). Interestingly, high expression of CLDN2 in the primary tumor was associated with a shorter time to recurrence at any site (HR=1.42; 95% CI=1.0-1.9) and with breast cancer specific death (HR=1.42; 95% CI=0.98-2.1). Specifically, high expression of CLDN2 in the primary tumor was associated with shorter progression to liver metastasis (HR=2.28; 95% CI=1.3-3.9). CLDN2 remained a significant prognostic factor for relapse free and liver metastasis free survival in multivariate analyses adjusting for known breast cancer prognostic factors. Furthermore, evaluation of CLDN2 expression in an independent cohort confirmed its negative prognostic value for early recurrences (HR=2.15; 95% CI=1.3-3.5).

Conclusions: These results suggest that the intrinsic subtypes of primary breast cancers are to a large extent maintained in recurrences, and further that liver metastases may be notably different and represent a distinct entity with a separate underlying biology compared to other metastases. In addition, a potential role of CLDN2 in the development of breast cancer liver metastases is highlighted and identifies CLDN2 as a novel negative prognostic factor in breast cancer which specifically predicts time to liver recurrence.

Citation Format: Siker Kimbung, Mårten Fernö, Per Malmström, Thomas Hatschek, Ingrid Hedenfalk. Claudin-2 is an independent negative prognostic factor in breast cancer and specifically predicts early liver recurrences. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B58.