Cryoablation for Malignant Bone and Soft Tissue Tumors and Histological Assessment of Ablated Tumors

Background/Aim: Cryoablation is a new, minimally invasive option for local tumor therapy that is attracting attention due to its potential interactions 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. Patients and 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 seven cases. 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 a 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. On histological examination, tissue in the ablated area was completely necrotic. In the border area between ablated and non-ablated areas, CD68-positive cells including CD16-M1-like and CD204-positive M2-like cells were more frequently observed than T cells. Conclusion: Cryoablation has shown good anti-tumor efficacy across various tumor types, including those affecting the bone. However, local control was inadequate for recurrent lesions and tumors larger than 4.0 cm in diameter. Further analysis of the relationship between macrophages and cryoablation is needed and may provide critical insights into achieving a more effective anti-tumor response.