Expression of contactin 4 is associated with malignant behavior in pheochromocytomas and paragangliomas

Context: Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine, usually benign, tumors. Currently, the only reliable criterion of malignancy is the presence of metastases. Objective: The aim of this study was to identify genes associated with malignancy in PPGLs. Design: Transcriptomic profiling was performed on 40 benign and 11 malignant PPGLs. Genes showing a significantly different expression between benign and malignant PPGLs with a ratio $4 were confirmed and tested in an independent series by quantitative real-time polymerase chain reaction (qRT-PCR). Immunohistochemistry was performed for the validated genes on 109 benign and 32 malignant PPGLs. Functional assays were performed with hPheo1 cells. Setting: This study was conducted at the Department of Pathology of the Erasmus MC University Medical Center Rotterdam Human Molecular Genetics laboratory of the de Duve Institute, University of Louvain. Patients: PPGL samples from 179 patients, diagnosed between 1972 and 2015, were included. Main outcome measures: Associations between gene expression and malignancy were tested using supervised clustering approaches. Results: Ten differentially expressed genes were selected based on messenger RNA (mRNA) expression array data. Contactin 4 (CNTN4) was overexpressed in malignant vs benign tumors [4.62-fold; false discovery rate (FDR), 0.001]. Overexpression at the mRNA level was confirmed using qRTPCR (2.90-fold, P=0.02; validation set: 4.26-fold, P=0.005). Consistent findings were obtained in The Cancer Genome Atlas cohort (2.7-fold; FDR, 0.02). CNTN4 protein was more frequently expressed in malignant than in benign PPGLs by immunohistochemistry (58% vs 17%; P=0.002). Survival after 7 days of culture under starvation conditions was significantly enhanced in hPheo1 cells transfected with CNTN4 complementary DNA. Conclusion: CNTN4 expression is consistently associated with malignant behavior in PPGLs.