(P 81) OPTIMIZING EWING SARCOMA AND OSTEOSARCOMA BIOPSY ACQUISITION: CONSENSUS RECOMMENDATIONS FROM THE CHILDREN'S ONCOLOGY GROUP BONE TUMOR COMMITTEE

Objective: Osteosarcoma and Ewing sarcoma are rare, aggressive bone and soft tissue sarcomas with peak incidence in adolescents and young adults. Novel risk-stratified treatment approaches for bone sarcoma are emerging and molecular profiling will be an essential component to inform future clinical trial enrollment and disease management. The procurement of sufficient tumor samples to facilitate downstream diagnostic, clinical molecular, and research-based testing are key to these efforts.
Percutaneous image-guided biopsy techniques have been increasingly employed for the diagnosis of primary bone tumors and confirmation of disease progression. Percutaneous procedures are less invasive and reduce recovery times, however potential limitations exist as the quantity and quality of tissue obtained through these procedures can vary. Further, sample processing requirements of bone tumors relative to other tumor types heightens the need for a standardized approach to tissue collection. As the bone tumor field moves toward an era of risk-stratified and molecular-based treatment options for patients, ensuring the acquisition of adequate tumor material is a priority. In this context, the Children’s Oncology Group (COG) Bone Tumor Committee details expert-vetted guidance for the acquisition and subsequent processing and storage of biopsy specimens for Ewing sarcoma and osteosarcoma.

Methods: The COG Bone Tumor Committee convened a multidisciplinary group of experts to evaluate available literature and institutional practices to generate guidance for the acquisition of suspected Ewing sarcoma and osteosarcoma biopsy material. The group included representation from oncology, pathology, orthopedic oncology, interventional radiology, basic science researchers and patient advocates. Members included representation from small, medium and large North American oncology programs to ensure. feasibility of universally implementing recommendations. Current and near-future biopsy tissue requirements were reviewed and are reflected in the consensus recommendations for pre-biopsy planning, percutaneous biopsy approaches and open biopsy approaches as well as biopsy tissue processing, allocation and storage.

Results: When a diagnosis or relapse of osteosarcoma or Ewing sarcoma is suspected, recommendations include pre-biopsy planning with a multidisciplinary team to ensure requisite tissue specimens are acquired and patient safety is prioritized. The biopsy location must be identified by the treating surgeon and planned in line with future incisions.
For core biopsies, we recommend the following: 15-20 16G 1.5-3cm cores for tumors with a soft tissue component; 5-7 12-13G cores for tumors without a soft tissue component and, when osteosarcoma is suspected, acquire an additional 2-3 12-13G cores of the underlying osteoid. This yield is anticipated to address all clinical and research/clinical trial-based needs including 2-4 blocks with 2-3 cores per block for clinical diagnostic needs, snap frozen tissue (~0.5 grams per vial), and fresh or viably frozen tumor material (Figure 1).
For open biopsies, a minimum of 1 cubic centimeter should be obtained. It is critical to adhere to principles for performing safe open biopsies including: use of a small longitudinal incision, maintenance of hemostasis, minimizing dissection, limited drain use and avoidance of neurovascular structures.
Pathology handling of bone biopsies is key. We suggest decalcifying tissue only if necessary. When necessary, we recommend the use of “soft decals” such as ETDA or ETDA/formic acid combinations for better preservation of nucleic acid integrity. For routine diagnostic processing, clinical tumor tissue specimens are fixed in formalin and embedded in paraffin (FFPE). While much improvement has occurred in the ability to extract nucleic acids from FFPE, there are some limitations to testing post-fixation. Therefore, it is beneficial to preplan the allocation of tissue for snap freezing, fresh tissue, and viable preservation of specimens with 10% DMSO-containing media.

Conclusion: This guidance reflects general approaches for consideration based on the perspective of clinical and scientific experts in the field in North America, with the understanding that individual clinical decisions regarding tissue acquisition must be made based on tumor location and patient condition. Identification of requisite tumor biopsy volumes and harmonization of pathology processing is paramount to prospective research validation efforts to advance both bone sarcoma clinical care and research. Further, novel therapeutic agents are routinely introduced with companion biomarkers, thus it is expected that molecular biomarker testing will become the standard of care. This perspective aims to serve as a reference to facilitate multidisciplinary harmonization in biopsy tissue acquisition (initial diagnosis and relapse specimens) and processing algorithms across institutions. Optimizing tissue collection to power innovative clinical trials informed by disease biology and to better understand treatment resistance mechanisms in advanced disease is paramount toward improving the care of children, adolescents and young adults diagnosed with Ewing sarcoma and osteosarcoma.