With the development of imaging equipment and interventional minimally invasive treatment technology, tumor ablation therapy has become a minimally invasive treatment method to rapidly inactivate tumor cells in situ and maximize the protection of normal tissues. Imaging-guided cryoablation, radiofrequency and microwave ablation have become indispensable tools for current tumor treatment. Ar-He knife cryoablation, as one of the means of tumor ablation therapy, has gradually received widespread attention because of its small trauma, good patient tolerance and wide range of indications, and now this technology has shown remarkable efficacy in solid tumor treatment. Development of argon helium knife ablation therapy Argon helium knife is an advanced technology for minimally invasive tumor treatment. Surgical resection has been the accepted treatment for tumors in the past, but about 70% of tumors are inoperable at the time of diagnosis, usually because the tumor site is critical, the boundary is unclear and the size is too large to be completely removed, or the patient is too old and frail to tolerate surgery, or the tumor has metastasized distantly and the opportunity for surgery is lost. Conventional radiotherapy and chemotherapy have limited effect on solid tumors and have high side effects, and the problems of drug resistance and therapeutic sensitivity in treatment are insurmountable barriers in clinical practice. Therefore, argon helium knife cryoablation, which aims to inactivate tumor cells in situ and eliminate tumor load, has been widely used. The Ar-He knife system can be used for precise ablation of tumors by percutaneous puncture under the guidance of ultrasound, CT or magnetic resonance imaging (MRI), which is less invasive, easier to perform, and does not interfere with the implementation of other comprehensive treatments. Ar-He knife ablation treatment principle The Ar-He knife uses a number of electronic computer and aerospace technologies such as argon cooling, helium heating, and timely monitoring. The thinnest tip of the Ar-He knife has an outer diameter of only 1.47 mm and is hollow and insulated. When circulating argon gas, the tip temperature instantly drops to minus 140°C, freezing tumor tissue into ice balls within minutes and causing tumor cells to rupture and necrosis. When helium is circulated, the tip temperature rises rapidly to 20~45℃, which melts the ice ball, disintegrates the tumor cells, and accelerates the degeneration and necrosis of the tumor tissue. This reversal of the cold and heat cycle completely destroys the cancerous tumor tissue, while the low temperature damages small blood vessels causing microcirculatory thrombosis which leads to tissue ischemia and necrosis. The body does not immediately remove the frozen necrotic tumor tissue, but the necrotic tissue can be used as antigen to activate and promote the body to generate anti-tumor immune response, enhance the body’s systemic immunity, initiate the immune killing effect on tumor cells, and further suppress the tumor. It has been reported that in a few cases, after in situ tumor cryo-inactivation, metastases in other sites also regressed, the mechanism of which has not been fully clarified. Characteristics of Ar-He knife ablation therapy Ar-He knife cryoablation, radiofrequency ablation and microwave ablation are all physical inactivation of tumors and are suitable for local solid tumors, regardless of whether the tumor tissue is rich in blood supply or not. The difference between the three is that argon helium knife is cryoablation, while radiofrequency and microwave are thermal ablation. Cryoablation has a wide range of indications. Because of the pain-relieving effect of cryoablation, local anesthesia can be used during the procedure, and general anesthesia is not required. Ar-He knife cryoablation can ablate lesions with a diameter of 10 cm or more by combining multiple needles and conformal freezing. Ablation with Ar-He knife is suitable for both benign and malignant tumors in all parts of the body, especially for elderly and frail tumor patients who cannot tolerate open surgery. For tumors <5 cm in diameter, ablation can be performed radically; for tumors >10 cm in diameter, ablation can be performed in stages to gradually inactivate the tumor and achieve optimal results with other comprehensive treatments. Ar-He knife treatment is suitable for the following tumors. 1.Respiratory system: primary lung cancer, metastatic lung tumors, mediastinal tumors, primary or metastatic tumors of the pleura. 2.Urological system: prostate tumor, kidney tumor, primary or metastatic tumor of adrenal gland. 3.Gastrointestinal system: primary and metastatic liver cancer, residual lesions after interventional embolization of liver cancer, various benign tumors of liver, rectal cancer. 4.Skin: skin tumor, hemangioma. 5.Skeletal system: primary or metastatic bone tumors. 6.Nervous system: various neurogenic tumors. 7.Muscular system: myofibroma, rhabdomyosarcoma. 8.Reproductive system: perineal tumor, cervical cancer, ovarian cancer, penile cancer. 9.Other: retroperitoneal tumor, fatty (sarcoma) tumor, breast cancer and tumor recurring after surgery. Efficacy of argon helium knife ablation therapy The killing of tumor tissues by argon helium knife cryoablation is non-selective, and all cells will undergo necrosis when the temperature is below -40℃. Under the guidance of CT and MRI, argon helium knife has achieved satisfactory efficacy in the treatment of lung, liver and kidney tumors, and has made promising progress in the treatment of benign tumors such as prostate hyperplasia and uterine fibroids. After 5 years of follow-up, the results showed that there was no significant difference in survival, local recurrence rate and metastasis rate between the two groups compared with the early conventional surgical resection group, suggesting that argon helium knife cryoablation therapy is an effective minimally invasive treatment method for intermediate and advanced liver cancer. The current study confirmed that most of the lesions with diameters <5 cm can be completely ablated at one time; for lesions with diameters >10 cm, satisfactory results can be achieved by fractionated ablation; combining cryoablation with molecular targeted therapy and immunotherapy can not only improve patients’ prognosis, but also prolong their survival. This shows that cryoablation with Ar-He knife provides a new and effective means for tumor treatment, and also opens up a new direction for clinical research on minimally invasive tumor treatment. Ar-He knife ablation technology, like all current tumor treatment methods, cannot achieve 100% cure of tumors. Clinical experience suggests that, in the comprehensive tumor treatment model, after cryoablation with Ar-He knife, it is necessary to cooperate with corresponding systemic treatment methods for subclinical lesions and potential residual cancer cells throughout the body. For patients with mid- to late-stage tumors, different comprehensive treatment options have been clinically proposed for how to address local tumor residuals after palliative treatment, such as argon helium knife combined with interventional embolization chemotherapy for mid- to late-stage liver cancer, combined chemotherapy for metastatic tumors, and combined Chinese medicine and immunotherapy for mid- to late-stage tumors. For tumors near the mediastinum, hepatoportal, bile duct and spinal cord, it is difficult to achieve complete ablation of the tumor by Ar-He knife freezing, which can be combined with radioactive particle placement to achieve the ideal effect of focal inactivation. The efficacy of Ar-He knife for local tumor control is well established, and the combination of this technique with other local and systemic therapeutic techniques can also improve the long-term outcome of patients. In conclusion, argon helium knife cryoablation therapy is less invasive, more efficient, more widely used, and more effective. It inactivates tumor tissues while preserving the functions of normal organs to the greatest extent possible, and it is easy to operate and has few postoperative complications for patients, and does not affect the choice of other comprehensive treatment measures.