Imaging and intervention for soft tissue tumours in the era of locoregional therapies and immunotherapy.

As part of a multidisciplinary team, clinical radiology plays key roles in the diagnosis, staging and treatment response assessment for soft tissue sarcoma (STS) and desmoid tumours (DTs), typically using a combination of ultrasound and magnetic resonance imaging (MRI) modalities. There is an increasing role for interventional radiology in the treatment of recurrent and oligometastatic disease in these tumour types. This clinical radiology review is aimed primarily at non-specialist cross-sectional consultant radiologists and more junior radiology consultants/specialist trainees with a special interest in musculoskeletal oncology. The existing role of F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) and MRI for assessment of treatment response in STS and DT, including the emerging role of whole-body MRI is outlined. Response metrics including Response Evaluation Criteria in Solid Tumors 1.1 (RECIST 1.1), modified RECIST, Positron Emission Tomography Response Criteria in Solid Tumours (PERCIST), immune Response Evaluation Criteria in Solid Tumors, iPERCIST and non-perfused volume ratio are also discussed in context. We introduce the potential role for locoregional therapies (LRTs), including microwave, cryotherapy and therapeutic ultrasound-based treatments as adjunctive treatments for selected cases within the current UK guidelines. We discuss the potential of high intensity focused ultrasound and other LRTs to release sarcoma tumour antigens systemically with the potential to enhance anti-tumour immunity (the 'abscopal' effect). With increasing indications and availability of locoregional therapies (LRTs) and the first indications of immunotherapy for selected subtypes of STS, potential future directions in functional imaging capability for STS and DT are also discussed.