Establishment and characterization of human choriocarcinoma cell line derived from a metastatic focus of a testicular mixed germ cell tumor.

A human testicular choriocarcinoma cell line HKRT-II was established by the single-cell cloning method from a mixed cell culture system derived from a retroperitoneal metastatic germ cell tumor composed of a yolk-sac tumor, a choriocarcinoma, and an immature teratoma. Its primary tumor rose from the testis and was comprised of a seminoma, a yolk-sac tumor, a choriocarcinoma and an immature teratoma. The HKRT-II cells were spindle or polygonal in shape and contained multi-nucleated giant cells showing neoplasticity and pleomorphism. The cells proliferated in a stable manner, and the population doubling time was 42 hours. The chromosome numbers showed a wide distribution of aneuploidy, while the mode was in the hypertetraploid range. Double minute chromosomes and homogeneously staining regions were recognized in about 5% to 10% of the metaphase plates, respectively. Heterotransplantation was not difficult. Subcutaneous transplantation of 1 x 10(7) cells into nude mice formed a tumor composed of only a choriocarcinoma. The most noteworthy characteristics of the cell line were that it produced human chorionic gonadotropin (hCG) in an in vitro culture system and in in vivo grafted cells, and that the N-myc gene was amplified about 10 times.