Cryoablation for malignant bone and soft tissue tumors and histological assessment of ablated tumors

Abstract

Background: Recurrent or metastatic disease after completion of initial therapy for primary sarcoma represents a substantial problem, along with as well as metastasis of cancer. Cryoablation is a new, minimally invasive option for local antitumor therapy that is attracting attention regarding relationships with the immune system. The purpose of this study was to evaluate the efficacy of cryoablation for local control of bone and soft tissue lesions, to elucidate risk factors for recurrence, and to clarify histological changes of necrosis and immune cell invasion after cryoablation. Methods: Participants comprised 25 patients who underwent cryoablation for 53 discrete lesions of bone or soft tissue recurrence after resection or as metastases of cancer or sarcoma. Local progression-free survival was evaluated after completion of cryoablation. The histology of tumor tissues resected after cryoablation was assessed for 7 cases. Tumor tissues after cryoablation was resected for 7 cases. H&E staining and immunostaining for CD4, CD8, CD68, CD16, CD204, IDO, and CD47 were performed. Results: Local progression-free survival rates were 88.1% at 1 year and 79.7% at 2 and 3 years. Risk of local progression was significantly higher for recurrent lesions after resection, and for lesions ≥4.0 cm in diameter than for metastatic lesions, or lesions <4.0 cm, respectively (p<0.05 each). In subgroup analysis of bone lesions, lesions with an extraskeletal component tended to be associated with worse local recurrence-free survival than those without an extraskeletal component (p=0.135). On histological examination, tissue in the ablated area was completely necrotic. In the border area between ablated and non-ablated areas, CD68-positive cells were more frequently observed than T cells. CD16-M1-like and CD204-positive M2-like cells were observed. Conclusions: Cryoablation demonstrated good anti-tumor efficacy without distinction of tumor types and bone. Local control for recurrent and lesions ≥4.0 cm in diameter was inadequate with cryoablation. Further analysis for the relation between macrophage and cryoablation is needed and may provide critical information about a superior anti-tumor effect.