(P 306) THERMAL NECROSIS IN ORTHOPAEDIC BONE TUMORS

Objective: Heat may be used as an adjuvant therapy in orthopaedic tumor cases with intent to induce thermal necrosis. Common methods include polymethylmethacrylate (PMMA; bone cement) which sets through an exothermic reaction, radiofrequency ablation, and laser thermal cautery. PMMA may be used to fill defects after intralesional excision of bone tumors, and for fixation of arthroplasty components. However, the question remains as to the degree of clinically relevant tumor necrosis that may be induced by thermal adjuvants.

Methods: We elected to test the effects of thermal stress on cell survival and viability on an array of 12 cell lines representing bone tumors and cancers which most commonly metastasize to the bone. A549 (adenocarcinoma), A498 and FU-UR-1 (renal cell carcinoma), PC3 (prostate cancer), MDA-MB-231 and MCF7 (breast cancer), MG-63 (osteosarcoma), K1 (papillary thyroid carcinoma), GCT (giant cell tumor), TT (thyroid medullary carcinoma), MM (multiple myeloma), SW 1353 (chondrosarcoma) cells, along with HEK293 (control; primary embryonic human kidney). Cells were subjected to heat stress via heating for 5 or 10 minutes on a heat block at 37, 42, 47, 50, 56, 60, 75, 90, or 100°C. Viability and proliferation were then assessed with crystal violet and MTT assays. The experiments were performed with technical and biological replicates.

Results: Although cell lines varied slightly in their sensitivity to heat stress, heating for 5 minutes at 75°C or 10 minutes at 60°C was sufficient to render 96-100% of cells non-viable when measured at 24 hours post heat stress. Thyroid, giant cell, and prostate cancer cell lines were the most sensitive to heat stress, followed by breast and lung cancer cells, with renal and bone cancers the least sensitive of the tested cancer cell lines.

Conclusion: These results are in line with previously described thresholds for thermal bone necrosis of 56°C, but demonstrate that a significant portion of cancer cells are able to remain viable until higher temperatures of 60-75°C are reached. While PMMA compounds Depuy SmartSet, Zimmer Palacos R, and Zimmer Palacos can exceed 60°C, other brands (such as Smith & Nephew Versabond) do not. This factor of heat as adjuvant therapy in orthopaedic tumor cases should be considered when choosing PMMA compounds or other forms of heating to induce thermal necrosis in marginal tumor cells.