(P 142) CORE NEEDLE BIOPSY OF PERIACETABULAR CHONDROSARCOMA OFTEN RESULTS IN UNDER-GRADING BUT DOES NOT CHANGE MANAGEMENT BY EXPERIENCED ORTHOPAEDIC ONCOLOGISTS.

Objective: There is discrepancy in the histologic concordance of pre-operative biopsy and post-surgical resection grading of periacetabular chondrosarcoma. This discrepancy poses a question as to whether the treatment may differ depending on the initial assessment of the tumor grade. The objective of this study was to evaluate the histologic concordance of pre-operative biopsy and post-surgical resection histological grading of periacetabular chondrosarcoma at a single institution. Furthermore, a secondary objective of this study was to determine whether institutional protocol should be modified to include open biopsy following a preoperative biopsy revealing a low-grade cartilaginous lesion to confirm the true nature of the tumor prior to proceeding with wide resection.

Methods: This is a retrospective review of patients with periacetabular cartilaginous tumors treated between 2000 and 2022 at a single institution. All patients included in the analysis underwent surgical resection. The pre-operative biopsy and post-surgical resection histological grades were compared. Concordance and treatment implications were evaluated.

Results: Twenty-two preoperative Image Guided Core Needle Biopsies (IGCNB) were performed. There was concordance between pre-operative and post-surgical resection histological grade in 9 cases, giving a (9/22) 40.9% accuracy rate. In total there were 13 cases of discrepancy between pre-operative biopsy and post-surgical resection histological grading. In 12 cases of discrepancy, post-surgical resection histology revealed a higher grade than that of pre-operative biopsy histology. In one case of discrepancy, pre-operative IGCNB biopsy histology revealed a high-grade chondrosarcoma while the post-surgical resection histology revealed an intermediate-grade. There were no situations in which the plan made based on a preoperative biopsy resulted in an inappropriate treatment decision, even when there was not concordance between preoperative diagnosis and diagnosis after definitive resection.

Conclusion: In conclusion, pre-operative biopsy often results in under grading, but it does not change management. The presence of cartilaginous tissue on preoperative biopsy from the periacetabular region, independent of grade, combined with correlative clinical and imaging features evaluated by experienced orthopaedic oncologists at a high-volume sarcoma center, can be used to guide treatment for suspected chondrosarcoma. When the imaging suggests a higher-grade tumor than the biopsy, the investigators of this paper treat the patient assuming a higher-grade tumor. Unlike treatment management of the upper and lower extremities, the investigators of the study treat all cartilage malignancies in the periacetabular region with wide resection, regardless of grade, due to the aforementioned tumor under grading.