Histological and immunohistochemical findings in experimental rhabdomyosarcomas. Comparisons between original tumors, tumor recurrences and allotransplants in nude mice

Abstract

Cellular heterogeneity, a regular property of malignant neoplasms, can constitute the basis for phenotypic shifting in malignant tumors. A disturbance of the balanced interactions as happens as result of all therapy measurements between tumor cell subpopulations and between tumor and host offers the possibility to profound changes on the basis of cellular heterogeneity. As tumor model we used methylcholanthrene-induced murine rhabdomyosarcomas, which were allotransplanted into nude mice. The original as well as the allotransplanted sarcomas were submitted repeated operative tumor mass reductions, comparable to an insufficient tumor surgery in man. The histology and the cellular differentiation were evaluated by light microscopy and immunohistochemical marker expression (vimentin, desmin and myoglobin). Our findings document that primary tumors, their recurrences after incomplete tumor removal, and allotransplants inclusive of their surgically induced recurrences were histologically and immunohistochemically not identical in every case when compared with each other, but despite the experimental procedures they retained basic criteria necessary for the rhabdomyosarcoma diagnosis. Changes in sarcoma histology and cellular marker expression are not only reflected by dedifferentiation but can also comprise differentiation (maturation) processes. After artificial breakdown of intratumoral cellular interactions and tumor/host relations, unknown sarcoma inherent factors directed to retaining basic properties obviously preponderate, at least for the moment, over accidental new cell clones with differing phenotypic characteristics, which could be expected by cellular heterogeneity and would result in a markedly changed tumor.