Footnotes

• Contributors All four co-authors contributed substantially to the conception of the work; the acquisition, analysis and interpretation of data for the work. Specifically EH and EM conducted a literature review pertaining to the topic which was used to inform the Background and Discussion sections in particular. These sections were later edited by the entire team of authors with a particular contribution from MH who was responsible for the overall care of the patient and whose expertise in the management of osteosarcoma guided the investigations, treatment and follow-up. The Case presentation and Investigations sections were initially drafted by EM under the guidance of MH, both of whom had the most contact with the patient. EH contributed substantially to this section in coordinating all of the imaging and figures from radiology and pathology departments. PM provided much of the advice and information pertaining to specific biochemical aspects of bhCG secretion throughout all sections of the paper and created the hCG graph. Each of the authors had read extensively and independently on the topic and drafted and revised the manuscript critically and approved the final version before submission. EH is responsible for the overall content as guarantor.

• Competing interests None declared.

• Patient consent Obtained.

• Provenance and peer review Not commissioned; externally peer reviewed.