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11524 Background: The Children’s Oncology Group (COG) Biorepository at the Biopathology Center (BPC), Nationwide Children’s Hospital, Columbus, OH contains archived tumor specimens submitted for COG study protocols. The BPC repository is utilized for numerous biology study aims with the goal of improved understanding of tumor pathophysiology, and impacts future clinical trials design and patient care. BPC pathologists perform quality assurance (QA) reviews of archival material before biospecimens are released for study. Since QA reviews are not routinely included in the submission process into the BPC, the quality and utility of tissue is often unclear. Therefore, a pathology quality assurance review was conducted to explore the utility of future testing on banked formalin fixed paraffin embedded (FFPE) Ewing Sarcoma and Osteosarcoma specimens. Methods: The BPC staff retrieved archival tumor cases for review between 06/2020 and 1/2022. One hematoxylin and eosin-stained slide per FFPE tissue block was digitally scanned for whole slide image (WSI) analysis and uploaded with a de-identified pathology report on a virtual slide-viewing platform. Five board certified pediatric pathologists with sarcoma expertise (AA, JB, SC, AS, JD) designed a digital QA review form and performed reviews. The QA review data collection form included diagnosis, volume of viable tumor, decalcification techniques, ancillary molecular/cytogenetic studies and a comment box to include additional noteworthy information. Results: During the study period, of the 1379 digitally prepared cases, 486 case reviews were completed, totaling 1192 digital slides reviewed. Of the reviewed cases, 465 (95%) were concordant with the diagnosis and had variable volumes of viable tumor (scant to adequate), while 33 (7%) of cases had no viable tumor (extensive necrosis or no tumor on the slide) and 21 (4%) had an alternative diagnosis (e.g. tumor submitted as osteosarcoma, re-classified as a chondromyxoid fibroma). Of the reviewed concordant cases, 271 (58%) were consistent with OS, 187 (40%) were consistent with ES and 7 (2%) were consistent non-ES round cell sarcomas (e.g. BCOR or CIC- rearranged sarcomas). Conclusions: Over ninety percent of reviewed specimens passed QA review, whereas the remaining failed due to diagnostic discordance or lack of viable tumor. Among cases with diagnostic concordance, variable volumes of tumor were present, including cases with scant viable tumors. Although QA reviews are time consuming, these results suggest QA reviews at tissue submission could potentially improve tissue quality available and timeliness of sample delivery for research. In addition, it would provide an opportunity for follow-up with sites to request submission of higher quality specimens and mitigate storage of tissue without potential for future use.