HIFU Ablation of Soft Tissue Sarcoma

Tissues that can be affected by soft tissue sarcomas include fat, muscle, blood vessels, nerves, deep skin tissues, tendons and ligaments. Sarcoma accounts for 1% of all cancer diagnoses; around 3,300 people are diagnosed with soft tissue sarcoma (STS) each year in the UK. The incidence of STS is unusual for cancer in that a relatively large proportion can occur in children and young adults, with 9% of cases in the under 30-year group and only 43% of cases in the 65 and over group. Whilst STS is rare, it remains a significant cause of morbidity and mortality. Prognosis is typically poor, with a five-year overall survival of approximately 54%.

The Oxford Bone and Soft Tissue Tumour Service at the Nuffield Orthopaedic Centre, Oxford, is a nationally approved tertiary referral centre for the treatment of soft tissue and primary bone sarcomas, receiving 400 new patient referrals annually. These patients are currently treated via a multidisciplinary approach involving expert radiologists, surgeons, clinical oncologists and histopathologists.

At our centre, patients with smaller (<5cm) STS proceed directly to surgical resection; this provides a low-risk opportunity to evaluate safety, feasibility and efficacy of novel pre-operative non-ionising ablative technologies, such as High Intensity Focused Ultrasound (HIFU). Patients with larger (>5cm) resectable STS currently receive neoadjuvant radiotherapy within six weeks of surgery, in line with national guidelines (Dangoor, 2016). Upon recurrence within the radiotherapy field (in-field recurrence), radiotherapy has high morbidity, including complications such as poor wound healing and infection (Tsagozis, 2018), and is not indicated prior to further surgical resection. Thus, in resectable cases of in-field recurrence, there is further opportunity to evaluate non-invasive HIFU, anticipated to both reduce tumour size and tumour vascularity, facilitating subsequent surgical resection. Furthermore, recurrent STS or metastatic STS not suitable for surgery have limited treatment options, and if not suitable for further chemo- or radio-therapy, HIFU may provide an alternative treatment option before palliation.

HIFU is a versatile treatment modality capable of destruction of tumours by focusing ultrasound waves from outside the body, usually through the medium of water, to cause ablation at a precise anatomical location.

It has demonstrated an impressive safety profile by virtue of being both non-invasive and lacking radiation, leading to FDA approvals for several indications including pain relief in bone metastases (Scipione, 2018) and uterine fibroids. Previous studies using an ultrasound-guided therapeutic device in China have demonstrated that HIFU is a successful treatment modality for soft tissue sarcoma (Yu, 2019), but this treatment has currently not been widely investigated within the UK's health care setting.

The University of Oxford and the Oxford University Hospitals NHS Trust have extensive clinical HIFU experience. The first extracorporeal HIFU device in Europe was used for a study performed at the Churchill Hospital between 2002 and 2004 (Illing, 2005). The study used an ultrasound-guided HIFU system (Model-JC Tumour Therapy System, HAIFU Technology Company Ltd, Chongqing, China) to treat 30 patients with tumour deposits in the kidney or liver and demonstrated both safety and efficacy. This was followed by a non-randomised Phase II clinical trial of HIFU ablation of liver tumours (Leslie, 2008), which compared radiological response against histological findings and again demonstrated safety and feasibility for non-invasive treatment of solid tumour deposits. These studies have led to CE-marking of the JC and JC-200 treatment devices for non-invasive treatment of solid tumours such as liver cancer, kidney tumours, breast cancer, bone tumours, pancreatic tumours and uterine fibroids, based on previous clinical trials at our unit (Lyon, 2019), the latter indication recently receiving NICE approval for US-guided HIFU ablation.

Safety and efficacy of HIFU has already been demonstrated for sacral chordoma in our institution (Gillies, 2016). Due to the highly targeted capabilities of HIFU, whilst leaving superficial skin and pre-focal tissues unharmed, the ablative technology may have a role in treating local recurrence following previous neoadjuvant radiotherapy. For example, following recurrence, HIFU may be able to facilitate conversion from amputation for local control to limb salvage surgery.

Desmoid tumours are a relatively poorly understood subtype of STS which are benign and do not metastasise. However, this tumour subtype demonstrates characteristics of aggressive fibromatosis and comes with significant morbidity and mortality due to their locally invasive nature and, in the familial form, typical bowel involvement. Treatment options are limited and poorly evaluated; mortality is 34% in patients undergoing surgery for intra-abdominal desmoid and post-resection recurrence rates for abdominal wall and intra-abdominal desmoids are 41% and 71% respectively (Sturt, 2006). By virtue of not disrupting the tissue planes, promoting further fibromatosis, HIFU has previously been used on desmoid tumours in small case series outside the UK and have demonstrated encouraging outcomes for both extra- and intra-abdominal desmoid tumours (Shi, 2016), (Ghanouni, 2017).

HIFU is an attractive treatment modality for these indications due to its excellent safety profile, versatility in treating a range of tumour locations (Shim, 2016), its capability to treat multiple smaller tumours in a single session and, furthermore, being repeatable due to the lack of ionising radiation. Oxford has over two-decades of world-class expertise in clinical HIFU with published experiences in translational research of many benign and malignant solid tumour subtypes (Iling, 2005), (Lyon, 2019), (Gilies, 2016), (Leslie, 2012), (Lyon, 2018), (Wu, 2004), (Kennedy, 2004). As the Chinese JC200 device used in Oxford uses diagnostic ultrasound through a water bath to target tumours, rather than an integrated MRI tunnel, treatment of tumours at a variety of anatomical locations becomes both more practical and financially economical.

The clinical HIFU service is complimented by an extensive pre-clinical therapeutic ultrasound research facility at the Institute of Biomedical Engineering, University of Oxford. This laboratory has provided expertise in treatment planning for a previous HIFU clinical trial using patient specific models which employ CT data (Gray, 2019). The multidisciplinary team of co-investigators and other researchers in Oxford have world-class expertise in academic and musculoskeletal radiology, sarcoma surgery, sarcoma radiotherapy and oncology, clinical histopathology and immunology.

Thus, in Oxford there is a unique opportunity to explore the utility of preoperative HIFU in the ablation of infield recurrent STS, smaller STS and desmoid tumours as a pilot study. The primary outcome measure of the study will be safety and feasibility. Radiological response will be explored as a secondary endpoints of efficacy using cross sectional (MRI) and functional imaging (18F-FDG PET), incorporating both size, perfusion and metabolic activity. In addition, novel MRI sequences (DWI including whole body MRI, CEST) may also be explored with the academic radiology department, which pose minimal addition risk to the patient (Chetan, 2019), (Schmidt, 2009).

Crucially, post-resection histology will permit histopathological correlation, mitigating against the possibility of falsely reassuring radiological evaluations (false positive complete ablations). Tertiary endpoints will explore immune response, which HIFU has been demonstrated to mediate (Wu 2004), (Wu, 2016), both through circulating blood markers and immunohistochemistry. This is of importance, as whilst this study may demonstrate safe and effective ablation of targeted STS tumours, there may be micro-metastases or known metastases elsewhere which may limit the overall survival. Thus, thorough understanding of the immune mechanisms at play during HIFU ablation may inform future complimentary systemic treatments. Whilst one other centre has recently published early HIFU experience in STS [6], we believe our proposed study will be the first to elucidate immune mechanisms in HIFU-ablation of STS, and the first trial of HIFU for STS in Europe.

Pain scores and quality of life metrics will also be captured both pre- and post-HIFU and this qualitative data can be used to demonstrate that the HIFU procedure was acceptable to the patient.