mechanical FUS ablation resulted in a systemic anti- tumour immune response and that the response is related to dendritic cell activation. The advantage of a systemic anti- tumour immune response is attack of residual tumour cells at the primary treatment site, but also potentially suppres- sion of distant metastases. Another potential therapeutic application is FUS- mediated gene transfer [63]. One of the key challenges in cancer gene therapy is spatial and temporal control of transgene expression in the tumour cells. In animal models FUS-induced hyperthermia has been successfully used to induce precise focal transgene expression in targeted tumour tissue [64]. This has been achieved by using a heat-sensitive promoter, usually the heat shock protein (hsp)70B promoter and a reporter gene, such as green fluoresecent protein (GFP) or firefly luciferase (Fluc) for in vivo monitoring of accuracy and effectiveness of FUS- mediated transgene expression [65]. Future research will focus on FUS hyperthermia-induced activation of a therapeutic (trans) gene, such as tumour necrosis factor α or interleukin 12. FUS hyperthermia has also been studied in animal models for targeted chemotherapy to solid tumours. Since conven- tional chemotherapeutic regimens cause systemic toxicity, developing strategies for improved targeted chemotherapeu- tic delivery is of great clinical interest. One method used for targeted chemotherapy is the use of heat-sensitive liposomes. In this method the chemotherapeutic drug is encapsulated in the liposome, which results in prolonged intra-vascular circulation time. Because malignant tumours are associated with neo-angiogenesis resulting in leaky vessels, liposomes will preferentially accumulate in the interstitium surrounding the tumour [66]. FUS-induced hyperthermia will enhance both extravasation and drug release when these heat- sensitive liposomes are used [67, 68]. Contrary to these studies that have shown enhanced drug delivery using FUS, results of a recent study assessing FUS for enhanced uptake of liposome-encapsulated doxorubicin in a mouse breast cancer model were disappointing [69]. Further studies are required to investigate the exact mechanisms by which FUS 1439 hypethermia may induce targeted drug release and define which therapeutic agents should be used. Conclusion FUS ablation has the potential to become an important modality for non-invasive image-guided treatment of localized breast cancer. Multiple phase I studies have proven MRI-guided and US-guided FUS ablation of breast cancer to be technically feasible and safe. The reported efficacy of FUS ablation as measured by percentages of complete tumour necrosis ranged from 20% to 100%. The difference in outcome between FUS ablation studies can be explained by differences in patient selection, imaging techniques, and tumour ablation protocols used. Although the results of US-guided and MRI-guided FUS ablation are promising, the data are too scant to justify a randomized controlled trial that compares FUS ablation with breast- conserving surgery for treatment of localized breast cancer. To date, MRI-guided treatment protocols of breast tumours offer the most accurate imaging technique for breast tumour targeting, breast tumour delineation, treatment monitoring (including temperature mapping), and detection of residual disease after treatment. The next step towards clinical implementation of FUS for breast tumour ablation would be a large prospective treat-and-resect study that assesses the therapeutic efficacy of MRI-guided FUS ablation in patients with small (<2 cm) solitary breast cancers and provides data that can be used for technique standardization and guideline formulation. 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