Bone metastasis is a prevalent complication of malignant tumors, often resulting in restricted mobility, severe pain, and diminished quality of life [1]. Pain represents the most frequent symptom of bone metastasis [2]. Inadequate pain management is particularly prevalent among patients with bone metastases; approximately 80% of cancer-related pain originates from bone metastases, and as many as 25% of patients report insufficient symptom control [3]. In addition, chronic pain can cause depression and anxiety [4,5]. Currently, numerous treatment options exist for managing pain associated with bone metastases, including systemic therapies (chemotherapy, hormonal therapy, radiopharmaceuticals, and bisphosphonates), various analgesics, local interventions (radiotherapy, laser-induced interstitial thermotherapy, and ablation therapy), and surgical approaches [6-8].

Currently, the most prevalent form of local ablation used in analgesic treatment includes techniques such as radiofrequency ablation, cryoablation, and microwave ablation. These methods have been extensively validated for their safety and analgesic effect [9,10]. However, each modality has inherent limitations. Hyperthermic ablation techniques (radiofrequency ablation and microwave ablation) may be constrained by heat-sink effects and carry a risk of thermal injury to adjacent structures [11,12], whereas cryoablation, although allowing improved visualization of the ice ball, does not permit needle tract ablation.

Chinese scientists have developed a co-ablation system that combines elements of hyperthermic ablation and cryoablation, using liquid nitrogen and alcohol as thermal media. The system is capable of achieving temperatures as low as −196 °C in freezing mode and up to approximately 80 °C in heating mode. The system operates by sequential application of freezing and heating, delivering extreme temperature changes to the target tissue. This design is intended to provide controlled thermal injury through alternating cold and heat exposure. Previous studies have demonstrated its effectiveness in cancer treatment [13,14].

However, there is currently limited literature documenting the use of a co-ablation system for the analgesic treatment of bone metastases. To address this knowledge gap, we conducted a retrospective exploratory study to assess the effectiveness and safety of the co-ablation system in managing pain associated with bone metastases.

In this retrospective single-arm exploratory study, the use of the co-ablation system was feasible and well tolerated in patients with bone metastases, with no procedure-related AEs observed. A reduction in pain intensity was noted over the follow-up period, with NRS scores showing a statistically significant overall decrease and most patients achieving a clinically meaningful pain reduction by week 4. Improvements in functional status, as reflected by KPS scores, were observed at later follow-up time points; however, these findings should be interpreted cautiously given the small sample size and study design. No patients required escalation of analgesic therapy during follow-up, and some were able to reduce their baseline analgesic doses. Collectively, these preliminary findings support the technical feasibility and short-term safety of the co-ablation system for palliative pain management in bone metastases.

Several studies have reported favorable pain control outcomes following ablation for bone metastases. Ma et al [18] evaluated microwave ablation, radiofrequency ablation, and cryoablation in patients with bone metastases from non-small cell lung cancer and observed a substantial reduction in pain scores at 4 weeks after treatment. Consistent with these findings, our study demonstrated a marked decrease in NRS scores over time, with median pain scores declining from baseline to 4 weeks after the procedure and most patients achieving a clinically meaningful pain reduction. Although an early reduction in pain was observed as soon as 1 day after treatment in our cohort, this change did not reach statistical significance, which may be related to the small sample size. In contrast, Yang et al [19] reported significant pain relief within 1 day following cryoablation; however, pain was assessed using a visual analog scale rather than NRS, which may limit direct comparability. Additionally, Tomasian et al [20] reported sustained pain relief at 3 months after ablation for painful vertebral metastases, a finding that aligns with the maintained reduction in NRS scores observed through 12 weeks in our study. Taken together, these observations suggest that the co-ablation system may offer pain control outcomes comparable to established ablation modalities, although direct comparisons should be interpreted cautiously.

High-intensity focused ultrasound is a noninvasive image-guided ablation technique that has demonstrated a favorable safety profile and promising analgesic effects in patients with painful bone metastases [21]. Previous prospective studies have shown that magnetic resonance–guided high-intensity focused ultrasound (MR-HIFU) can achieve rapid and clinically meaningful pain reduction without treatment-related AEs [22,23]. Bongiovanni et al [22] reported complete or partial pain responses in all treated patients at 30 days, whereas Napoli et al [23] observed significant improvements in pain severity and interference, with additional evidence of local tumor response in some cases. Although MR-HIFU differs from the co-ablation system evaluated in this study in terms of invasiveness and ablation mechanism, both approaches support the role of targeted local ablation in pain palliation. In our cohort, short-term pain relief without ablation-related AEs was observed, which is consistent with the analgesic and safety trends reported for MR-HIFU.

Previous studies have shown that multimodality approaches combining local ablation with radiotherapy, vertebroplasty, or iodine-125 seed implantation can improve pain control in patients with bone metastases [24-26]. These findings suggest that co-ablation could potentially be incorporated into multimodal palliative strategies in future practice and investigation. In our study, we also observed that the dosage of analgesic drugs was significantly reduced in some patients following the procedure. This finding is consistent with previous reports indicating a reduction in analgesic requirements after cryoablation [19,20,24,27].

Following treatment with the co-ablation system, patients demonstrated a gradual improvement in functional status, as reflected by increasing KPS scores over the follow-up period. Although no statistically significant improvement was observed at 1 week after treatment, KPS scores improved significantly from 4 weeks onward and remained stable through 12 weeks. These findings are in line with the MOTION (Multicenter Study of Cryoablation for Palliation of Painful Bone Metastases) study, which reported that cryoablation provided rapid pain relief while functional status was maintained and quality of life improved during follow-up [28].

This study is limited by its small sample size and retrospective, single-arm design; these factors reduce statistical power, limit generalizability, and preclude adjustment for pain-related confounders. Patient heterogeneity in primary tumors and metastatic sites, as well as the absence of a comparative control group, prevents assessment of relative efficacy vs established ablation modalities. The 12-week follow-up period was sufficient for short-term pain assessment but inadequate for evaluating the durability of response, pain recurrence, or delayed AEs. Pain from untreated disease sites may have influenced NRS and KPS scores, and the use of KPS without patient-reported outcome measures provides limited insight into overall quality of life.

In this small retrospective exploratory study, the co-ablation system was technically feasible and well tolerated in patients with painful bone metastases. Pain reduction was observed during short-term follow-up, and functional performance was maintained or gradually improved, with no procedure-related AEs recorded. These preliminary findings support further evaluation of the co-ablation system in larger, prospective controlled studies.