Cancer clinical researches using heat-generating nanoparticles have been conducted in four Japanese universities including authors' universities. The nanoparticles were injected intratumorally and its heat generation was induced by external magnetic field irradiation to kill cancer cells. Three kinds of composite magnetites nanoparticles were applied to clinical researches in combination with either types of magnetic field irradiators generating different frequencies. In this paper we reviewed results of these researches with our unpublished data and discussed its potential and further refinement.

Critical issues of clinical feasibility were not found in key process of treatment such as nanoparticles injection, magnetites imaging and magnetic field irradiation. A combinational use of magnetite cationic liposomes (MCL) and alternating magnetic field (AMF) irradiator was found to exhibit tumor regression activity without adverse events such as skin burn and histological damages of surrounding normal tissues. However, efficacies were found variable among tumors whose temperature rise was commonly achieved. In order to ensure efficacy, we discussed importance of MCL dosage divided by tumor volume (mg/cm3) and proposed total heat dose divided by tumor volume (J/cm3) as candidate index to control clinical treatments.

Microwaves (frequency: 0.3–300 GHz) have the ability to heat materials according to their dielectric properties and are used in microwave ovens for heating food and to yield improvements in the synthesis of medicine and decomposition of environmental pollutants, among other applications. In the medical field, microwaves have been used in cancer treatments such as hyperthermia and microwave coagulation therapy, and favorable treatment results have been obtained. Cancer treatments also have advantages for various types of cancers and have few serious side effects. In contrast, in cancer cell death by microwave heating, the cells are reportedly killed via different pathways compared with that by normal heating. In the future, the treatment efficiency needs to be improved, and the associated side effects can be reduced by analyzing the cell death mechanism in detail. In this review, we outline the latest methods of microwave cancer therapy and introduce the mechanism of cancer cell death by microwave irradiation with a focus on authors' reports.