**5. Conclusions**

In conclusion, personalized medicine is especially challenging and important in this patient group with strongly impaired survival rates. Therefore, accurate information about individual patient prognosis should be pursued before individual patient managemen<sup>t</sup> decision making. Next to clinical and pathological characteristics, biological tumor characteristics such as metabolic parameters on [18F]FDG-PET scans can be considered for this purpose. In this regard, the current study finds SUVmax and SUVpeak to be significantly predictive for overall survival in patients with metastases from STS. Furthermore, both features add prognostic value to the best performing clinical parameters.

**Author Contributions:** Conceptualization, G.M.K., W.G. and L.-F.d.G.-O.; methodology, G.M.K., W.G., J.L.B. and L.-F.d.G.-O.; software, G.M.K. and F.H.P.v.V.; validation, G.M.K., W.G. and F.H.P.v.V.; formal analysis, G.M.K., W.G. and L.-F.d.G.-O.; investigation, G.M.K., J.V.M.G.B., H.G., J.A.v.d.H., M.A.J.v.d.S., J.L.B. and L.-F.d.G.-O.; resources, G.M.K., J.V.M.G.B., H.G., J.A.v.d.H., M.A.J.v.d.S., F.H.P.v.V., J.L.B. and L.-F.d.G.-O.; data curation, G.M.K., W.G., J.V.M.G.B. and L.-F.d.G.-O.; writing— original draft preparation, G.M.K. and L.-F.d.G.-O.; writing—review and editing, G.M.K., W.G., J.V.M.G.B., H.G., J.A.v.d.H., M.A.J.v.d.S., F.H.P.v.V., J.L.B. and L.-F.d.G.-O.; visualization, G.M.K., F.H.P.v.V. and L.-F.d.G.-O.; supervision, W.G., J.L.B. and L.-F.d.G.-O.; project administration, G.M.K.; funding acquisition, W.G., J.L.B. and L.-F.d.G.-O. All authors have read and agreed to the published version of the manuscript.

**Funding:** We declare the following financial interests/personal relationships which may be considered as potential competing interests: G.M. Kalisvaart was the recipient of an educational gran<sup>t</sup> from Philips Electronics Nederland B.V, Eindhoven, The Netherlands, during writing of this manuscript. Furthermore, the research presented in the manuscript was supported by a public gran<sup>t</sup> from Health~Holland TKI Life Sciences & Health.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethics Committee Leiden Den Haag Delft (METC LDD) (protocol code: B19.050, date of approval 14 January 2020).

**Informed Consent Statement:** Patient consent was waived due to due to the retrospective nature of the study. Patients who objected to the use of their data were excluded.

**Data Availability Statement:** The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

**Acknowledgments:** The authors would like to thank Jan W. Schoones for his contribution to the search strategy.

**Conflicts of Interest:** The authors have declared that no competing interest exist.

## **Appendix A. Literature Search**

A systematic literature search was performed to identify available articles describing original research attending to our hypothesis. A search strategy based on our hypothesis was designed with the assistance of a medical librarian and conducted in PubMed on 1 September 2021. A total of 182 records were identified. After screening the titles, 32 records were excluded. In addition, after reading the abstracts and/or full articles, another 150 records were excluded. No articles that investigated our hypothesis were found (Figure A1).

Search strategy: (("advanced soft tissue sarcoma"[tw] OR "advanced soft tissue sarcomas"[tw] OR "advanced sarcoma"[tw] OR "advanced sarcomas"[tw] OR "metastatic soft tissue sarcoma"[tw] OR "metastatic soft tissue sarcomas"[tw] OR "metastatic sarcoma"[tw] OR "metastatic sarcomas"[tw] OR "metastasized sarcoma"[tw] OR (("soft tissue sarcomas"[tw] OR "soft tissue sarcoma"[tw] OR (("Sarcoma"[Mesh:NoExp] OR "sarcoma"[tw] OR "sarcomas"[tw]) AND ("soft tissue"[tw] OR "soft tissues"[tw])) OR "Adenosarcoma"[mesh] OR "Carcinosarcoma"[mesh] OR "Fibrosarcoma"[mesh] OR "Hemangiosarcoma"[mesh] OR "Histiocytoma, Malignant Fibrous"[mesh] OR "Leiomyosarcoma"[mesh] OR "Liposarcoma"[mesh] OR "Lymphangiosarcoma"[mesh] OR "Mixed Tumor, Mesodermal"[mesh] OR "Myosarcoma"[mesh] OR "Myxosarcoma"[mesh] OR "Sarcoma, Alveolar Soft Part"[mesh] OR "Sarcoma, Clear Cell"[mesh] OR "Sarcoma, Myeloid"[mesh] OR "Sarcoma, Small Cell"[mesh] OR "Sarcoma, Synovial"[mesh] OR "Adenosarcoma"[tw] OR "Adenosarcomas"[tw] OR "Alveolar Soft Part Sarcoma"[tw] OR "Alveolar Soft Part Sarcomas"[tw] OR "Carcinosarcoma"[tw] OR "Carcinosarcomas"[tw] OR "Clear Cell Sarcoma"[tw] OR "Clear Cell Sarcomas"[tw] OR "Dermatofibrosarcoma"[tw] OR "Dermatofibrosarcomas"[tw] OR "Fibrosarcoma"[tw] OR "Fibrosarcomas"[tw] OR "Hemangiosarcoma"[tw] OR "Hemangiosarcomas"[tw] OR "Leiomyosarcoma"[tw] OR "Leiomyosarcomas"[tw] OR "Liposarcoma"[tw] OR "Liposarcomas"[tw] OR "Lymphangiosarcoma"[tw] OR "Lymphangiosarcomas"[tw] OR "Malignant Fibrous

Histiocytoma"[tw] OR "Malignant Fibrous Histiocytomas"[tw] OR "Mesodermal Mixed Tumor"[tw] OR "Mesodermal Mixed Tumors"[tw] OR "Mesodermal Mixed Tumour"[tw] OR "Mesodermal Mixed Tumours"[tw] OR "Myeloid Sarcoma"[tw] OR "Myeloid Sarcomas"[tw] OR "Myosarcoma"[tw] OR "Myosarcomas"[tw] OR "Myxosarcoma"[tw] OR "Myxosarcomas"[tw] OR "Neurofibrosarcoma"[tw] OR "Neurofibrosarcomas"[tw] OR "Rhabdomyosarcoma"[tw] OR "Rhabdomyosarcomas"[tw] OR "Small Cell Sarcoma"[tw] OR "Small Cell Sarcomas"[tw] OR "Synovial Sarcoma "[tw] OR "Synovial Sarcomas"[tw] OR "Walker Carcinoma 256"[tw]) AND ("Neoplasm Metastasis"[Mesh] OR "Metastasis"[tw] OR "metasta\*"[tw] OR "advanced"[tw]))) AND ("FDG-PET"[tw] OR "FDG-PET"[tw] OR "18FDG-PET"[tw] OR "18FDGPET"[tw] OR "Positron-Emission Tomography"[Mesh] OR "Positron-Emission Tomography"[tw] OR "Positron-Emission"[tw] OR "PET"[tw] OR "PETCT"[tw] OR "Fluorodeoxyglucose F18"[Mesh] OR "Fluorodeoxyglucose F18"[tw] OR "FDG"[tw] OR "18F-FDG"[tw] OR "Fluorodeoxyglucose F 18"[tw] OR "Fludeoxyglucose F 18"[tw] OR "Fluorine 18 fluorodeoxyglucose"[tw] OR "18F Fluorodeoxyglucose"[tw] OR "18FDG"[tw] OR "2 Fluoro 2 deoxy D glucose"[tw] OR "2 Fluoro 2 deoxyglucose"[tw] OR "4-fluoro-4-deoxyglucose"[Supplementary Concept]) AND ("Mortality"[Mesh] OR "mortality"[Subheading] OR "Disease-Free Survival"[Mesh] OR "Survival Analysis"[Mesh] OR "Survival Rate"[Mesh] OR "Progression-Free Survival"[Mesh] OR "mortality"[tw] OR "survival"[tw] OR "death"[tw] OR "deaths"[tw] OR "Prognosis"[Mesh] OR "Prognosis"[tw] OR "prognos\*"[tw] OR "outcome"[tw] OR "outcomes"[tw]) NOT (("Case Reports"[ptyp] OR "case repor<sup>t</sup>"[ti]) NOT ("Clinical Study"[ptyp] OR "trial"[ti] OR "RCT"[ti]))).

**Figure A1.** Flowchart of the performed literature search.
