Frequent EGFR expression/EGFR amplification and lack of activating mutation in testicular choriocarcinoma

Choriocarcinoma (CC) is the rarest but most aggressive histological component of adult testicular germ cell tumor (TGCT). Although we previously reported a putative role of epidermal growth factor receptor (EGFR) alterations in the progression of CC, little is known about the kinase-activating mutation status of EGFR, which predicts the response to EGFR-tyrosine kinase inhibitors. In this study, we clinicopathologically reviewed a total of 12 cases of mixed TGCTs with CC components. Immunohistochemistry, fluorescence in situ hybridization, and direct sequencing was performed to investigate EGFR expression, EGFR copy number alterations, and functional mutation of EGFR in these CC components, respectively. Four (33%) of 12 cases exhibited predominant CC components (>50%), and all these patients died due to disease within 62 months. Overexpression of EGFR, higher copy number of EGFR, and amplification of EGFR was observed in 12 (100%), 10 (83%), and 9 (75%) of 12 CC components, respectively. None of the cases showed any mutational events in exons 18 to 24, which encode the tyrosine kinase domain of EGFR. These results confirm an important role of EGFR in the tumor aggressiveness of testicular CCs and may suggest its possible innate resistance against conventional anti-EGFR therapies.