Retrospective audit of 957 consecutive 18F-FDG PET-CT scans compared to CT and MRI in 493 patients with different histological subtypes of bone and soft tissue sarcoma.

Background: The use of ¹⁸F-FDG PET-CT (PET-CT) is widespread in many cancer types compared to sarcoma. We report a large retrospective audit of PET-CT in bone and soft tissue sarcoma with varied grade in a single multi-disciplinary centre. We also sought to answer three questions. Firstly, the correlation between sarcoma sub-type and grade with ¹⁸FDG SUVmax, secondly, the practical uses of PET-CT in the clinical setting of staging (during initial diagnosis), restaging (new baseline prior to definitive intervention) and treatment response. Finally, we also attempted to evaluate the potential additional benefit of PET-CT over concurrent conventional CT and MRI.

Methods: A total of 957 consecutive PET-CT scans were performed in a single supra-regional centre in 493 sarcoma patients (excluding GIST) between 2007 and 2014. We compared, PET-CT SUVmax values in relation to histology and FNCCC grading. We compared PET-CT findings relative to concurrent conventional imaging (MRI and CT) in staging, restaging and treatment responses.

Results: High-grade (II/III) bone and soft tissue sarcoma correlated with high SUVmax, especially undifferentiated pleomorphic sarcoma, leiomyosarcoma, translocation induced sarcomas (Ewing, synovial, alveolar rhabdomyosarcoma), de-differentiated liposarcoma and osteosarcoma. Lower SUVmax values were observed in sarcomas of low histological grade (grade I), and in rare subtypes of intermediate grade soft tissue sarcoma (e.g. alveolar soft part sarcoma and solitary fibrous tumour). SUVmax variation was noted in malignant peripheral nerve sheath tumours, compared to the histologically benign plexiform neurofibroma, whereas PET-CT could clearly differentiate low from high-grade chondrosarcoma. We identified added utility of PET-CT in addition to MRI and CT in high-grade sarcoma of bone and soft tissues. An estimated 21% overall potential benefit was observed for PET-CT over CT/MRI, and in particular, in 'upstaging' of high-grade disease (from M0 to M1) where an additional 12% of cases were deemed M1 following PET-CT.

Conclusions: PET-CT in high-grade bone and soft tissue sarcoma can add significant benefit to routine CT/MRI staging. Further prospective and multi-centre evaluation of PET-CT is warranted to determine the actual predictive value and cost-effectiveness of PET-CT in directing clinical management of clinically complex and heterogeneous high-grade sarcomas.