EHMT2/G9a and EZH2: Epimarkers in testicular germ cell tumors

Testicular germ cell tumors remain the most frequent solid malignancies in young males. Despite excellent prognosis, the fact that only 60% of patients at diagnosis have elevated serum tumor markers (dependent on stage and histology) and the poor quality of life of patients who develop resistance to chemotherapy cannot be neglected. Consequently, it is mandatory to bring out novel biomarkers.

The main goal was to evaluate EZH2 and EHMT2/G9a immunoexpression in a well-characterized patients' cohort of primary and metastatic testicular germ cell tumors, seeking associations with clinicopathological features and discovering differential immunoexpression patterns among specific subtypes.

First, an in silico analysis of the Cancer Genome Atlas database was performed regarding EZH2 and EHMT2/G9a. Then, immunohistochemistry for EZH2 and EHMT2/G9a was carried out in a cohort of testicular germ cell tumor patients, comprising 155 chemo-naïve primary tumors and 11 chemo-treated metastases. Immunoexpression was evaluated using a digital pathology analysis software.

Higher EZH2 and EHMT2/G9a expression levels were found in non-seminoma in the in silico analysis, particularly in embryonal carcinoma. Through digital pathology analysis, non-seminomas showed significantly higher EZH2 and EHMT2/G9a immunoexpression, with embryonal carcinoma showing higher expression. Moreover, mixed tumors with 50% or more of embryonal carcinoma component revealed the highest nuclei positivity for both biomarkers. Cisplatin-exposed metastases demonstrated a higher EZH2-positive nuclei and H-score, as well as higher EHMT2/G9a-positive nuclei.

Overall, our data suggest that EZH2 and EHMT2/G9a might be associated with greater aggressiveness and, eventually, involved in the metastatic setting, paving the way for testing targeted therapies.