The changed profile of tumour cells under radiation might be associated with biological changes of tumour subpopulations in view of radioresistance and metastatic potential and might be useful to identify intercellular regulation mechanisms and to define parameters being predictive for a response to therapy.

Background Heterogeneity in human malignant tumors is a well‐described phenomenon and of interest with regard to subpopulations with differences in clonality, metastatic potential, and response to therapy under different treatment regimes. The aim of this study was the simultaneous characterization of surface markers and DNA content of solid tumors to identify tumor cell subpopulations and to study the association between the expression of antigens and DNA content. Methods In the present study, six different malignant tumors grown as xenografts in nude mice were characterized by five‐parameter flow cytometry. Immunophenotyping was performed using a variety of direct fluorescence‐conjugated antibodies. In all cases, simultaneous detection of DNA content was done after staining with 7‐aminoactinomycin D. Results Tumor cells were characterized by light scatter properties, antigen expression, and DNA content. Tumor cell heterogeneity, subpopulations, and DNA content‐dependent antigen expression were identified. Conclusions This method offers the possibility of characterizing solid tumors according to their immunophenotype and DNA content. The results obtained can be used to identify changes in immunophenotypic and DNA profiles of tumor cell populations before and after therapy and might be useful to define parameters predictive for response to therapy. Cytometry 41:172–177, 2000 © 2000 Wiley‐Liss, Inc.

The observed radiation-induced changes of cytokine and receptor profile are an indication for complex intercellular interactions in view of radioresistance-associated mechanisms between cell populations within one individual tumour. The observed heterogeneous response on radiation might have therapeutic implications for an individualized therapy based on combined radiation and cytokine modulation, defined by flow cytometric characterization of markers potentially informative for radioresistance.