BACKGROUND: Combined protocols of radiation therapy and surgical resection, as applied in advanced oral cancer, rely on objective and early assessment of treatment response to radiation therapy. Non-responders require immediate radical salvage surgery even in spite of substantial operative risks, while complete or subtotal response may give reasons for continuing the conservative approach. Therefore, we investigated radiation response by FDG-PET for early monitoring of oral cancer. PATIENTS AND METHODS: In 30 patients with advanced stages of oral cancer (Table 1), FDG-PET (Siemens, ECAT EXACT 922) was performed within 4 weeks after completion of preoperative radiation therapy (36 Gy). SUV of tumor regions were compared to the histologic degree of tumor regression in complete resection specimens. Statistic evaluation included correlation analysis of SUV vs tumor regression and ROC analysis for SUV cut-off values. RESULTS: While low FDG accumulation was found in tumors with histological complete remission (2.3 +/- 0.4) as well as in cases of residual tumor (3.4 +/- 1.8), high FDG uptake was a rather specific indicator of vital tumor tissue (Figure 2). Significant correlation (p = 0.045) between postradiotherapeutic FDG-uptake and histological tumor regression was recognized. A SUV > 2.75 as a clinically practicable threshold value for the identification of residual vital tumor resulted in a specificity of 88%, sensitivity of 68%, a positive predictive value of 94% and a negative predictive value of 50% (Figure 3). Based on our actual follow-up data we could not confirm a significant correlation between postradiotherapeutic SUV and patients' survival. CONCLUSION: Within a standardized protocol, FDG-PET recognize treatment response to radiation therapy in oral squamous cell carcinoma with a reasonable specificity and thus provides a basis for further therapeutic decisions. An increased SUV (> 2.75) may be the rational to justify an aggressive surgical approach even when patients face substantial surgical or anesthesiological risk. However, the posttherapeutic pattern of glucose uptake varies with the applied treatment modalities and has to be explored for the protocol applied.