Inclusion Criteria:  --------  The participant is eligible for the study if they are:  Willing and able to give informed consent for participation in the study.  Aged 18 years or above.  Diagnosed with histologically-confirmed and HIFU-targetable soft tissue sarcoma of several subtypes, including but not necessarily limited to:  Malignant fibrous histiocytoma Undifferentiated (pleomorphic) sarcoma Fibrosarcoma and fibromyxoid sarcoma (fibroblastic sarcomas) Leiomyosarcoma Liposarcoma Malignant peripheral nerve sheath tumour Retroperitoneal sarcoma Rhabdomyosarcoma Synovial sarcoma Desmoid tumours (intra-abdominal, including extra-peritoneal tumours which involve the abdominal wall)  Have at least one of the following:  Untreated or recurrent primary resectable STS tumour 1-5cm diameter, targetable by HIFU Infield recurrent primary resectable STS tumour of >1cm diameter, targetable by HIFU Primary or metastatic STS unsuitable for resection or further chemo- or radiotherapy, targetable by HIFU Small (1-8cm) symptomatic intra-abdominal desmoid tumour, targetable by HIFU, which is unsuitable for surgery (or patient has previously refused surgery)  Have life expectancy of over 12 months and a World Health Organisation (WHO) performance status of less than or equal to 1.  Be able to attend Churchill Hospital and Nuffield Orthopaedic Center, Oxford, potentially for multiple visits, and thus be based in the UK.  Willing to allow his or her GP and Consultant to be notified of participation in the study.  Able and willing to give written informed consent, indicating that they are aware of the investigational nature of this study and potential risks, and able to comply with the protocol for the duration of the study, including scheduled follow-up visits and examinations.  Exclusion Criteria:  --------  The participant may not enter the study if ANY of the following apply:  Diagnosed with histologically confirmed Osteosarcoma or Chordoma  Diagnosed with histologically confirmed soft tissue sarcoma of the following subtypes:  GIST Chondrosarcoma Kaposi's sarcoma Ewings sarcoma Giant cell tumour Angiosarcoma  Active medical or psychological illness that would render the patient unsuitable for the interventions required for the study (exclusion at the discretion of the investigator).  Pregnancy.  Ulceration / skin breakdown / erythema overlying the target tumour site due to tumour invasion (exclusion at the discretion of the investigator).  Significant radiation skin damage overlying the target tumour site (exclusion at the discretion of the investigator).  Impractical anatomical locations for HIFU targeting (using JC200 treatment device) (exclusion at the discretion of the investigator):  Retroperitoneum Skull Neck Axilla Foot  Unfavourable imaging features on previously acquired cross-sectional imaging, including:  Tumour within 1cm of the skin surface Interposition (or close proximity) of a gas-containing structure between tumour and skin such as fixed (retroperitoneal) bowel or lung Interposition of a continuous ossified bone between tumour and skin, such as coverage by pelvis or scapula Tumour margin close (<1.5cm) or encasing major neurovascular bundles (such as the sciatic nerve) Tumour margin close (<1.5 cm) to critical visceral structures (e.g. bladder or bowel)  Recent radiotherapy (under 6 months) to the target tumour site.  Recent surgery (under 6 weeks) to the target tumour site.  Have any known allergic reactions to intravenous imaging agents to be used in this study (exclusion at the discretion of the investigator).  Have contraindication(s) or intolerance to MRI (exclusion at the discretion of the investigator).  Current involvement in phase 1 studies.  Soft tissue sarcoma participants: Use of chemotherapy or of an investigational drug within 30 days or 5 half-lives, whichever is longer, preceding the intervention.  Desmoid participants: hormonal medication including the contraceptive pill or tamoxifen, or being treated with imatinib.