Aims. Cell-free DNA (cfDNA) and circulating tumour DNA (ctDNA) are used for prognostication and monitoring in patients with carcinomas, but their utility is unclear in sarcomas. The objectives of this pilot study were to explore the prognostic significance of cfDNA and investigate whether tumour-specific alterations can be detected in the circulation of sarcoma patients. Methods. Matched tumour and blood were collected from 64 sarcoma patients (n = 70 samples) prior to resection of the primary tumour (n = 57) or disease recurrence (n = 7). DNA was isolated from plasma, quantified, and analyzed for cfDNA. A subset of cases (n = 6) underwent whole exome sequencing to identify tumour-specific alterations used to detect ctDNA using digital droplet polymerase chain reaction (ddPCR). Results. Cell-free was present in 69 of 70 samples above 0.5 ng/ml. Improved disease-free survival was found for patients with lower cfDNA levels (90% vs 48% at one-year for ≤ 6 ng/ml and > 6 ng/ml, respectively; p = 0.005). Digital droplet PCR was performed as a pilot study and mutant alleles were detectable at 0.5% to 2.5% of the wild type genome, and at a level of 0.25 ng tumour DNA. Tumour-specific alterations (ctDNA) were found in five of six cases. Conclusion. This work demonstrates the feasibility and potential utility of cfDNA and ctDNA as biomarkers for bone and soft-tissue sarcomas, despite the lack of recurrent genomic alterations. A larger study is required to validate these findings. Cite this article: Bone Joint Res 2021;10(9):602–610

Objective. Clinical studies of patients with bone sarcomas have been challenged by insufficient numbers at individual centres to draw valid conclusions. Our objective was to assess the feasibility of conducting a definitive multi-centre randomised controlled trial (RCT) to determine whether a five-day regimen of post-operative antibiotics, in comparison to a 24-hour regimen, decreases surgical site infections in patients undergoing endoprosthetic reconstruction for lower extremity primary bone tumours. . Methods. We performed a pilot international multi-centre RCT. We used central randomisation to conceal treatment allocation and sham antibiotics to blind participants, surgeons, and data collectors. We determined feasibility by measuring patient enrolment, completeness of follow-up, and protocol deviations for the antibiotic regimens. . Results. We screened 96 patients and enrolled 60 participants (44 men and 16 women) across 21 sites from four countries over 24 months (mean 2.13 participants per site per year, standard deviation 2.14). One participant was lost to follow-up and one withdrew consent. Complete data were obtained for 98% of eligible patients at two weeks, 83% at six months, and 73% at one year (the remainder with partial data or pending queries). In total, 18 participants missed at least one dose of antibiotics or placebo post-operatively, but 93% of all post-operative doses were administered per protocol. . Conclusions. It is feasible to conduct a definitive multi-centre RCT of post-operative antibiotic regimens in patients with bone sarcomas, but further expansion of our collaborative network will be critical. We have demonstrated an ability to coordinate in multiple countries, enrol participants, maintain protocol adherence, and minimise losses to follow-up. Cite this article: Bone Joint Res;4:154–162