VARIABILITY OF DIFFERENTIATION PATTERNS IN XENOTRANSPLANTED SPINDLE-CELL SARCOMAS - A HISTOMORPHOLOGICAL, IMMUNOHISTOCHEMICAL, AND ULTRASTRUCTURAL-STUDY

Three leiomyosarcomas, 3 nerve sheath sarcomas, 1 rhabdomyosarcoma, an d 1 sarcoma not otherwise classifiable with 17 of their xenografts, gr own on nude mice, were analyzed to assess the degree of concordance be tween histomorphology, immunohistochemistry, and ultrastructure in spi ndle cell sarcoma xenograft differentiation. Histomorphology was incon clusive or misleading in 4/8 sarcoma strains and immunohistochemistry in 4/8 originals and in 10/17 xenografts, although specific patterns h ad been identified ultrastructurally. Electron microscopy was superior to immunohistochemistry and histomorphology in spindle cell sarcoma d ifferential diagnosis. A further purpose of this study was to clarify whether spindle cell sarcoma xenografts retain the morphological chara cteristics of their primaries. Histomorphological features of the prim aries were preserved over all passages, whereas the immunohistochemica l marker profiles as well as the ultrastructural phenotypes changed in 14/17 xenografts and in 8/17 xenografts, respectively. Moreover, unus ual bidirectional or tridirectional patterns of differentiation were i dentified ultrastructurally with leiomyomatous as well as Schwann cell s occurring side by side and with MFH-like areas in 5/17 xenotransplan ts. These findings suggest genetic instability of tumor cells and may be important in the consideration of mesenchymal differentiation pathw ays.