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Background: 5-Aminolevulinic acid (5-ALA), a fluorescent contrast agent, has been used for tumor paint and photodynamic therapy (PDT) for various tumors, but its use with soft tissue sarcomas is not well documented. Myxofibrosarcoma, a subtype of soft tissue sarcoma with a high local recurrence rate, may benefit from similar types of treatment. The purpose of this study was to analyze the effects of 5-ALA tumor paint and PDT on a myxofibrosarcoma cell line. Methods: Tumor paint was assessed by exposing micromass pellets of human adipose-derived stromal (ADS) cells or myxofibrosarcoma (MUG-Myx1) cells to 5-ALA. Cell pellets were then visualized using a microscope at established excitation and emission wavelengths. Corrected total cell fluorescence was calculated per accepted protocols. Photodynamic therapy was similarly assessed by exposing ADS and MUG-Myx1 cells to 5-ALA, with subsequent analysis via flow cytometry and real-time confocal microscopy. Results: The use of 5-ALA tumor paint led to a selective fluorescence in MUG-Myx1 cells. Findings were confirmed by flow cytometry. Interestingly, flow cytometry results showed progressive selective cell death with increasing 5-ALA exposure as a result of the PDT effect. PDT was further confirmed using confocal microscopy, which revealed progressive cellular bubble formation consistent with advancing stages of cell death—a finding that was not seen in control ADS cells. Conclusions: 5-ALA tumor paint and PDT were successfully used on a human myxofibrosarcoma cell line (MUG-Myx1). Results from this study showed both selective fluorescent tagging and selective cytotoxicity of 5-ALA toward malignant myxofibrosarcoma cells, while sparing benign adipose control cells. This finding was further confirmed in a dramatic time-lapse video, visually confirming active, targeted cell death. 5-ALA's two-pronged application of selective tumor identification and cytotoxicity may transform surgical and medical approaches for treating soft tissue sarcomas. [ABSTRACT FROM AUTHOR]