Tumor necrosis in osteosarcoma: Inclusion of the point of greatest metabolic activity from F-18 FDG PET/CT in the histopathologic analysis

Objective To determine if the location of the point of maximum standardized uptake value (SUVmax) being included in or not included in the histopathologic slab section corresponded to tumor necrosis or survival. Materials and methods Twenty-nine osteosarcoma patients underwent post-chemotherapy [fluorine-18]-fluoro-2-deoxy- D-glucose (FDG) positron-emission tomography-computed tomography (PET/CT) prior to resection. PET/CT images were correlated with slab-section location as determined by photographs or knowledge of specimen processing. The location of the point of SUVmax was then assigned as being 'in' or 'out' of the slab section. Cox's proportional hazard regression was used to evaluate relationships between the location and value of SUVmax and survival. Logistic regression was employed to evaluate tumor necrosis. Results No correlation was found between the SUVmax location and survival or tumor necrosis. High SUVmax correlated to poor survival. Conclusion High SUVmax value correlated to poor survival. Minimal viable tumor (> 10%) following chemotherapy is a known indicator of poor survival. No correlation was found between the location of SUVmax and survival or tumor necrosis. Therefore, the SUVmax value either does not correspond to a sufficient number of tumor cells to influence tumor necrosis measurement or it was included in the out-of-slab samples that were directed to viableappearing areas of the gross specimen. Since high SUVmax has been previously found to correspond to poor tumor necrosis, and tumor necrosis is simply an estimate of the amount of viable tumor, SUVmax likely represents many viable tumor cells. Therefore, when not in the slab section, SUVmax was likely included in the tumor necrosis measurement through directed sampling, validating our current method of osteosarcoma specimen analysis.