Assessment of Embryonic MicroRNAs and DNA Methylation Suggests That Chemotherapy Induces Differentiation of Germ Cell-Derived Trophoblastic Tumors

Unusual trophoblastic tumors of germ cell origin-epithelioid trophoblastic tumor (ETT), unclassified trophoblastic tumor (UTT), cystic trophoblastic tumor (CTT), and monophasic choriocarcinoma (MChorio)-are rare and mostly encountered postchemotherapy. Their relationship to other germ cell tumor types and gestational tumors remains uncertain. We used microRNA‑371~373 levels and DNA methylation profiling to compare nonchoriocarcinoma germ cell-derived trophoblastic tumors to gestational trophoblastic neoplasms and postpubertal-type teratoma. A total of 36 trophoblastic tumors of germ cell origin were included (biphasic choriocarcinoma [n=16], MChorio [n=4], CTT [n=9], UTT [n=6], and ETT [n=1]). MicroRNA‑371~373 levels were assessed by RT‑qPCR on germ cell-derived trophoblastic tumors and compared with nontrophoblastic testicular germ cell tumors and gestational trophoblastic tumors (n=50). DNA methylation profiling was performed using EPIC array on germ cell-derived trophoblastic tumors and compared with postpubertal-type teratomas and gestational trophoblastic tumors (n=28). Nonchoriocarcinoma trophoblastic tumors of germ cell origin showed significantly lower miR‑371a‑3p levels than germ cell-derived biphasic choriocarcinomas (P=0.0002). Compared with teratoma, differentiating trophoblastic tumors retained higher miR‑371a‑3p levels (P=0.0129). Analyses performed using the top differentially methylated probes revealed that CTT, UTT, and ETT of germ cell origin clustered with teratoma, while choriocarcinomas of germ cell origin clustered with gestational trophoblastic tumors. DNA methylation patterns showed increasing differentiation from choriocarcinoma toward teratoma-like profiles. Our results suggest that germ-cell-derived ETT, UTT, and CTT represent "differentiated" trophoblastic tumor phenotypes with similarities to teratoma, whereas germ-cell-derived choriocarcinomas resemble gestational trophoblastic tumors.