Characteristics of human soft tissue sarcomas in xenografts and in vitro

Two permanent, transplantable strains of rhabdomyosarcoma (SAS) and synovial sarcoma (KUSHI) were established by transplanting them serially into nude mice. The original SAS tumor and its transplant were histologically identical and gave an appearance of so-called embryonal rhabdomyosarcoma. The KUSHI tumor changed after the second passage, showing the biphasic pattern of synovial sarcoma, while undifferentiated myoblast-like cells were observed throughout the original tumor. Three in vitro cell lines from the SAS and one from the KUSHI tumor were successfully established. The human origin of the SAS and KUSHI transplanted tumors could be verified by the presence of human chromosomes. The cells cultured from the SAS tumor were more sensitive to anticancer drugs than those of the KUSHI tumor. However, as the number of serial passages on nude mice increased, the sensitivities of the SAS cells decreased, while those of the KUSHI cells increased. The modal chromosome number of the SAS tumor changed from 51 to 49 to 46 during serial passages on nude mice. These observations suggest that the sensitivities to anticancer drugs not only differ among soft tissue sarcomas of different histologic types, but also change continuously during the growth of the tumor itself.