Modern cryotherapy began in the 1960s when a neurosurgeon developed a modern cryosurgical system using a probe to treat brain tumors and movement disorders (20). Cryoablation is a hypothermic modality that induces tissue damage via a freeze-thaw process.

The cryoablation technique utilizes the Joule-Thomson effect by releasing compressed liquid gases into target tumor tissues via specialized cryoablation probes. As the compressed liquid gas rapidly expands and transforms into the gaseous state, it produces an ultra-low temperature, rapidly decreasing the target tissue temperature to about −140°C. Mechanisms of cell death initiated by cryoablation include direct cell damage caused by ice crystal formation, microcirculatory failure after thawing, and induction of apoptosis and necrosis (21).

Compared to other ablation techniques, cryoablation offers superior precision in controlling the freezing range, enabling selective tissue damage while minimizing collateral effects on surrounding nerves and blood vessels. The low-temperature environment not only reduces the risk of thermal injury, but also promotes faster post-ablation healing. Cryoablation preserves the native antigenic structure and exhibit the highest potential to elicit post-ablation immunogenic responses, it generates a more robust immune response than other ablation therapies (22).

However, cryoablation involves a longer duration because sufficient time is required for the cryogen to fully act on the target area, a process that may take several hours; the low temperatures may lead to platelet depletion, increasing the bleeding risk; thus, patients with poor coagulation function should avoid this treatment method. The debate persists over whether cryoablation holds an advantage over RFA and MWA (23).

The first application of RFA was reported in the early 1990s for liver tumor (49). This method uses radiowaves of low frequency (460–480 kHz) and long wavelength to generate heat within a tumor mass. It induces cell death by direct thermal damage and coagulative necrosis, and the extent of tissue damage depends on the conductance of the tissue (50).

The focal zone temperature of RFA can typically reach between 60°C to 100°C. When the temperature reaches above 60°C, tumor cells begin to experience irreversible thermal damage. Temperatures between 70°C to 100°C can more effectively destroy tumor cells, as such high temperatures can lead to denaturation of intracellular proteins and disruption of the cell membrane. At the same time, heat diffusion creates a transitional zone (42°C–60°C) near the focal zone, where sublethal temperatures induce apoptotic cell death. This process, if accompanied with disruption of cellular membrane integrity, may transition into ICD. The temperature range of 42°C to 45°C is generally considered the starting point for cell damage, which may lead to impaired cell function but not necessarily immediate lethality. In the temperature range of 45°C to 60°C, tumor cells begin to experience thermal damage, and as the temperature approaches 60°C, the cumulative effect of cell damage becomes more pronounced, with the required temperature and time for therapeutic effect also decreasing accordingly (51, 52).

However, it is difficult to maintain the cytotoxic temperature if the ablated tumor is close to the great vessels. This heat-sink effect is a commonly described limitation of RFA and occurs when heat absorbed by flowing blood or air carried away from the ablation zone, thereby dissipating heat and reducing RFA effectiveness (53). Prolonged heating can lead to tissue charring, which can limit the further penetration of the ablative energy, and it may not penetrate as deeply into tissue as other ablation therapies, potentially leaving behind viable tumor cells.

Inflammatory infiltrates, including neutrophils, macrophages, DCs, NK cells, and ablated tissue-specific B and T cells, not only increased in the transitional zone, but also have been observed in distant untreated tumors and the peripheral blood in animals and patients (52). The immune changes of RFA are generally less than that of cryoablation, for example, in colon cancer murine model, cryoablation augmented secretion of a wider array of cytokines including interleukin (IL)-1β, IL-5, IL-6, and IL-10 than RFA, with both anti-tumor and anti-inflammatory profiles (54). The changes in peripheral T cell subsets following RFA appear to be independent of the tumor type or hepatitis status (55).

Tabuse et al. first explored the application of MWA in treating liver cancer in 1986 (66). MWA uses heat generated by electromagnetic waves (frequency, 915 or 2450 MHz) to produce high temperatures (60–150°C), leading to tumor coagulation necrosis (67). It is associated with significantly reduced renal damage and is well tolerated in the case of large, inoperable lesions (68). MWA is less dependent on tissue characteristics, it can produce more accurate and larger ablation zones than RFA (69). The advancements in thermoacoustic imaging technology (70) will improve the effectiveness and application range of MWA. However, the ablation zones created by MWA can be less predictable and more spherical (71), which may not conform to the shape of irregularly shaped tumors. Although MWA is less affected by the heat sink effect than RFA, it still remains subject to this influence, especially around large blood vessels.

Compared to cryoablation and RFA, MWA induced relatively weak immune responses, with a significantly lower proinflammatory cytokine IL-1β and IL-6 production after MWA (72). Despite this, MWA combined with immunotherapy has emerged as a promising new direction in cancer therapy due to its technical feasibility, fewer side effects, and potential for synergistic effects in combination with immunotherapy, which can enhance the overall anti-tumor efficacy (73).

Edd et al. first reported the results of in vivo experiments that confirmed the feasibility of IRE in 2006. IRE is an emerging tumor ablation technique that induces tumor cell apoptosis via high-voltage direct current to produce multiple nanoscale micropores on cell membranes without damaging peripheral structures and tissues, such as the blood vessels and nerves (95). However, the efficacy of the treatment can be limited by the depth of the electric field penetration, potentially in sufficient for larger or deeply seated tumors. Additionally, in complex anatomical areas, the precision of the electric field delivery may be challenging to achieve.

IRE leads to the exposure of many autologous tumor antigens in situ (96). It may elicit stronger immune responses than RFA as well as MWA, because the advantage of preserving blood vessels contributes to the transmission of immune molecules or cells.

The effectiveness of HIFU on human localized prostate cancer in vivo was first reported in 1995 (107). It is a non-invasive, non-ionizing technique that uses focused ultrasound to produce areas of intense heat and cavitation, causing coagulative necrosis and mechanical cell damage. HIFU therapy for localized prostate cancer can achieve an oncologic control comparable to the conventional standard of care of, which includes radical prostatectomy and external beam radiation therapy, while reducing associated side effects caused by standard of care, such as incontinence and impotence (108). However, the penetration depth of HIFU is limited, which can make tumors located deep in the body less effective. Bone or air can scatter or absorb ultrasound energy, limiting the effectiveness of HIFU.

The immune response to HIFU is generally similar to RFA, but it can be influenced by the precise focusing and control of the ultrasound energy, potentially leading to a more localized immune reaction.

In 1990, Sugiyama et al. first reported that LITT was safe and effective in treating deep brain tumors (116). The development of MRI thermometry introduced a breakthrough in the widespread use of LITT in neurosurgery. LITT refers to the selective ablation of lesions or structures using heat released by a laser with superior precision and predictable tissue ablation volumes, thus avoiding collateral damage (117).

LITT is particularly useful in cases where the tumor is located in a difficult-to-access location or in patients considered risky for surgery. Nevertheless, the limited penetration depth of the laser beam restricts its suitability for treating larger or deeply located tumors. Similar to RFA, extended exposure to the laser’s energy can result in tissue charring, thereby limiting the effectiveness of the treatment.

The immune response is comparable to RFA, it can cause blood-brain barrier (BBB) disruption, enhance antigen presentation, improve the function of cytotoxic CD8⁺ T cells, and exert an immunostimulatory effect on the TME (118).

TACE is a minimally invasive interventional therapy in which a drug-loaded embolic agent is injected directly into the tumor-feeding artery to produce locoregional chemotherapy and embolization at the tumor site synergistically.

It can be performed with lipiodol (conventional, cTACE) or drug-eluting beads (DEB-TACE). DEB-TACE was reported to improve the drug loading capacity by absorbing high concentrations of electropositive chemotherapeutic agents; however, it did not appear to have an advantage over cTACE in terms of efficacy (131).

A systematic review of randomized trials involving unresectable HCC showed that TACE significantly improved the OS in comparison to the control group of conservative management (132). It is the first-line therapy for treating intermediate-stage B HCC, according to the Barcelona Clinic Liver Cancer Staging System (133, 134).

There are conflicting opinions on the effects of TACE on immune regulation. On the one hand, TACE promotes the release of tumor antigens and proinflammatory cytokines, promotes ICD, and converts non-immunogenic tumors into immunogenic tumors (135, 136). Ren et al. demonstrated that the Treg cell proportion after TACE was significantly lower in HCC patients, which indicated the positive regulatory effect on the anticancer immune function of HCC patients (137). On the other, hypoxia of residual tumor cells caused by incomplete embolization up-regulates vascular endothelial growth factor (VEGF) expression, which hinders DC maturation and function and increases the recruitment of Treg cells and MDSCs, resulting in immunosuppressive effects (138, 139). Hypoxia is an important cause of tumor recurrence and metastasis in HCC after TACE, by promoting tumor cell invasiveness, angiogenesis, drug resistance, metabolic changes, and the maintenance of tumor stem cell characteristics.

Therefore, the efficacy of TACE may be increased when combined with anti-VEGF antibody and ICI. A prospective, single-arm, phase 2 study of TACE combined with anti-PD-L1 antibody (envafolimab) and lenvatinib in unresectable HCC demonstrated promising survival outcomes and operable conversion rates with a tolerable safety profile (140). A global, open-label, phase 3 IMbrave150 trial established that treatment with atezolizumab plus anti-VEGF antibody (bevacizumab) resulted in better OS and PFS outcomes than sorafenib in patients with advanced HCC (141). Another phase 3 EMERALD-1 trial demonstrated that the combination of TACE with anti-PD-L1 antibody (durvalumab) and bevacizumab significantly improved the PFS (median, 15 vs. 8.2 months; HR (hazard ratio), 0.77; P = 0.032) in unresectable HCC patients compared with TACE alone; the PFS after treatment with TACE plus durvalumab was not significant (median: 10 vs. 8.2 months, HR 0.94, P = 0.638) (142).

A nationwide multicenter, retrospective cohort study comprising patients with advanced HCC, showed that first-line therapy with TACE plus ICI plus anti-VEGF antibody was associated with significantly longer OS (median, 22.6 vs. 15.9 months; HR, 0.63; P < 0.0001), PFS (median, 9.9 vs. 7.4 months; HR, 0.74; P < 0.0001), and ORR (41.2% vs. 22.9%; P < 0.0001) and acceptable safety profiles than treatment with ICI plus anti-VEGF antibody (143). This finding indicates that TACE plays an important role in the TACE-ICI-VEGF regime, which may be due to the effective reduction of the intrahepatic tumor burden by TACE, thereby improving the efficacy of ICI-VEGF.

Nanomaterials have emerged as a promising strategy in cancer immunotherapy with the advent of nanotechnology (144). Nanovaccines contain tumor antigens to which T cells specifically respond, immune adjuvants that enhance immune responses, and targeted delivery vaccine systems, such as ligand-directed targeting, molecular targeting, and pH-sensitive vesicles, which improve the sensitivity of immunotherapy (145). Shi et al. designed a nanovaccine that can synergize TACE, induce ICD of tumor cells under hypoxia, increase the infiltration of primary and distant tumor-toxic T lymphocytes, promote the maturation of DCs in lymph nodes, and activate potent antitumor immune responses (14). It improves hypoxia and immunosuppressive TME after TACE and prevents tumor recurrence and metastasis. In the long-term, sustained progress in biomimetic nanovaccines will help enhance existing technologies and potentially revolutionize the clinical landscape for cancer management.

The efficacy of TACE is severely limited by the inferior drug burst behavior, which is typically due to factors such as poor drug carrier design, material properties, and the insufficient biocompatibility, resulting in a lack of long-term drug release controllability, which affects its immune response (146). Ma et al. developed gelatin-based drug-eluting microembolics grafted with nanosized poly (acrylic acid), which exhibited vessel remodeling-induced permanent embolization with minimal inflammatory responses after complete degradation (147). This resulted in an effective and versatile strategy for enhancing the long-term therapeutic responses of various local chemotherapy treatments. Furthermore, the microembolics demonstrated optimal mechanical, pharmaceutical, and biological properties, with excellent micro-catheter deliverability in a healthy porcine liver model, and significantly augmented the TACE efficacy in a rabbit VX2 liver cancer model (147).

TARE uses yttrium-90 (Y90), administered via resin or glass microspheres. Local radiation causes direct DNA damage and tumor cell death by injecting radioactive microspheres into the hepatic artery (148). However, TARE is associated with radiation-related toxicity, and compared to TACE, its therapeutic effects typically manifest more slowly, which may be disadvantageous for rapidly progressing diseases.

TARE can be used to treat HCC and other primary and secondary hepatic malignancies, such as intrahepatic cholangiocarcinoma and hepatic metastases from neuroendocrine cancer, ocular melanoma, and breast cancer (149). The irradiated tumor cells affect the tumor microenvironment and may act as an immunogenic hub, inducing an abscopal effect. Chew et al. compared peripheral blood mononuclear cells before and after TARE and observed an infiltration of GZMB ⁺ cells, CD8⁺ T cells, CD56⁺ NK cells, and CD8⁺ CD56⁺ natural killer T (NKT) cells, with increased TNF-α levels and antigen-presenting cells after TARE (150). GZMB ⁺ cells can release GZMB, which primarily participate in cytotoxic immune responses and can induce apoptosis of tumor cells (151). Among NK cells, CD56⁺ NK cells typically possess a more effective ability to kill tumor cells and are also more prone to secreting cytokines such as IFN-γ and TNF-α (152). CD8⁺ CD56⁺ NKT cells possess both the cytotoxicity of T cells and the regulatory functions of NKT cells, they can recognize and eliminate tumor cells, while also regulating the immune response through the release of cytokines (153), thereby enhancing the tumor immune cycle, inducing ICD, and further eliciting an abscopal effect.

Next-generation sequencing confirmed the upregulation of genes involved in innate and adaptive immune activation in TARE-treated tumors. Young et al. evaluated 102 TARE treatments in 93 patients with HCC. Their findings revealed that patients with pretreatment absolute lymphocyte counts exceeding 1 × 10³/μL pretreatment demonstrated significantly longer OS at 1, 3, and 6 months post-treatment compared to those with counts below this threshold (154).

Deipolyi et al. analyzed the immune effect of TARE on liver metastases from breast cancer to assess the clinical utility of PD-1 levels (155). The clinical response was associated with an increase in baseline PD-1 expression by CD4⁺ TILs in the TME, highlighting the potential synergistic effect of TARE and anti-PD-1 antibodies in treating liver tumors. A retrospective case series of 11 patients with uveal melanoma-derived unresectable hepatic metastases demonstrated that TARE combined with anti-CTLA-4/PD-1 antibody is safe and effective (156). Another single-center retrospective study comprising 26 patients with HCC who received TARE with nivolumab and/or ipilimumab revealed a median OS of 16.5 months and PFS of 5.7 months from the first TARE, thus indicating that the combined regimen was safe with limited treatment-related toxicity (157).

These results promote prospective studies evaluating the combined regimen of TARE plus ICI for HCC treatment. In a Phase 1 clinical trial involving HCC patients, the disease control rate was 82% (N = 9/11) in the TARE plus nivolumab group (158). A Phase 2 trial of 36 patients with advanced HCC who received TARE followed by nivolumab showed an ORR of 30.6% (159). Further exploration is needed to determine the optimal time for administering the combined regimen.