Advancements in microwave ablation for tumor treatment and future directions

Abstract

Microwave ablation (MWA) is a minimally invasive treatment that uses thermal energy to target and destroy tumors. Compared to other ablation methods, such as radiofrequency ablation (RFA), MWA operates at higher frequencies, allowing for faster ablation and larger treatment areas. In addition to its direct tumor-destroying effects, MWA has been shown to activate immune responses, contributing to long-term antitumor effects. MWA can also be combined with surgery, chemotherapy, and immunotherapy to enhance treatment outcomes. This review examines the current research on MWA's technical innovations, clinical applications, and its potential in improving cancer treatment efficacy.

Keywords: Biomedical Engineering; Biotechnology; Medical Physics; Thermodynamical functions.

Graphical abstract

Figure 1

Overview of how MWA, RFA, and cryoablation work

Figure 2

Overview of microwave ablation technology Through various imaging methods, ablation probes that can emit microwave electromagnetic fields are guided into tumor tissues. Under the action of electromagnetic fields, polar molecules (mainly H₂O) in the tissues are forced to continuously rearrange with the oscillating electric field, thereby increasing their kinetic energy, rapidly raising the tissue temperature in a short time, and causing coagulative necrosis of the target tissues. In addition, MWA can also exert antitumor effects by eliciting an immune response or when combined with other treatment options.

Figure 3

Image guidance and evaluation during MWA (A) Ultrasound-guided MWA in the treatment of papillary thyroid carcinoma. (1) Preoperative contrast-enhanced (CE) ultrasound images showing a low-enhancement pattern of the tumor (arrow); (2) ultrasound images of the carotid artery and vagus nerve (arrow) surrounding the tumor were protected by hydrodissection technique (arrow); (3) hyperechoic pattern of the tumor during ablation (arrow); (4) The CE US image after ablation showed no enhancement of the tumor (arrow). (B) (1) Preoperative arterial CT axial flow imaging showed vascular liver cancer in section VIII of the liver; (2) the ablation margin on the right (star) side of the tumor was assessed as inadequate on intraoperative CT images after the expected ablation was completed. (3) Immediate supplementary ablation is performed by repositioning the MWA probe to cover areas with insufficient margins; (4) MRI assessed that the tumor (dashed line) was completely ablated. (C) MRI-guided MWA for the treatment of right upper lobe lung adenocarcinoma. (1) Guided by magnetic resonance imaging (MRI), skin markers were applied to locate the needle insertion site; (2) guided by magnetic resonance T1WI, 16G ablation antenna was inserted into the center of tumor lesion; (3 and 4) following two 8-min ablation cycles, tissue ablation areas were obtained, which can be clearly seen in axial (3) and sagittal (4) phase images with large areas of ground glass covering the entire tumor. The US, MRI, and CT images were adapted and reprinted under terms of the CC-BY license from Cao et al., Shen et al., and Joo et al., respectively. Copyright, 2021, Radiological Society of North America Inc. Copyright, 2022, Springer Verlag. Copyright, 2022, Frontiers Media S.A.

Figure 4

Application of nanomaterials in microwave ablation (A) Multifunctional nanospheres, when enriched in the tumor area, enhance the heating efficiency of MWA, significantly improving the speed and amplitude of heating, and also expand the ablation range. (B) Multifunctional nanospheres, when combined with MWA, can activate the body’s antitumor immune response, yielding a better therapeutic effect. (C) Multifunctional nanospheres used in conjunction with MWA can induce changes in specific gene pathways, enhancing antitumor efficacy.

Figure 5

Antitumor immune response induced by MWA After MWA treatment, there was an increase in the proportion of CD8⁺ T cells in the peripheral blood, a decrease in the proportion of Treg cells and the concentration of IL-2, an enhancement in the co-stimulatory properties of CD4⁺ T cells, an amplification in T cell clonality, and an improved interaction between B cells and CD4⁺ T cells. Additionally, MWA induced ICOS+ activated CD4⁺ T cells and a significant increase in serum interferon-gamma levels. It can also have abscopal effects on distant untreated tumors, resulting in upregulated expression of TIGIT and LAG3 in immune cells within those tumors. Combining MWA with TIGIT/LAG3 blockade can significantly enhance the expansion of CD8⁺ TILs and reshape the tumor microenvironment.^,