Bone and soft-tissue sarcomas — formative SAQs

SAQ 1 (10)

A fourteen-year-old boy presents with three months of deep aching pain in the distal right thigh, worse at night and unrelated to football. His mother now feels a firm swelling just above the knee. A plain radiograph shows a mixed lytic and sclerotic lesion in the distal femoral metaphysis with cortical destruction, perpendicular sunburst spicules and a triangular lifted periosteum. [1] [3]

a) Name the most likely diagnosis, and explain how each radiographic feature (the metaphyseal site, the mixed lytic and sclerotic matrix, the sunburst and the triangular periosteal reaction) supports it. (3 marks) [1]

b) State the local and distant staging investigations you would arrange, and justify the magnetic resonance imaging of the whole compartment and the computed tomography of the chest. (3 marks) [3]

c) A colleague offers to book the boy for an open excisional biopsy in the local theatre the next day. State the principle that governs the biopsy of a suspected sarcoma, the harm the unplanned biopsy causes, and where the biopsy should instead be performed. (2 marks) [1]

d) Outline the definitive treatment plan, naming the chemotherapy backbone, the timing of the surgery relative to the chemotherapy, and the role of the histologic response. (2 marks) [1][2]

SAQ 2 (10)

A four-year-old girl is brought with two weeks of a painless swelling beneath the right eye, progressive proptosis and a recently noticed squint. Magnetic resonance imaging shows an enhancing soft-tissue mass in the right orbit with no intracranial extension. The biopsy confirms an embryonal rhabdomyosarcoma. [4] [5]

a) Explain why the site and the histology place this child in a favourable prognostic group, and name the molecular marker that distinguishes the unfavourable subtype. (3 marks) [5]

b) State the standard chemotherapy backbone for rhabdomyosarcoma, and outline the role of surgery and radiotherapy in local control for this orbital lesion. (3 marks) [4]

c) A child with a bulky pelvic rhabdomyosarcoma is about to start chemotherapy. Define the laboratory tumour lysis syndrome using the Cairo-Bishop criteria, and state the prophylactic measures you would put in place before the first dose. (2 marks) [6]

d) Frame the prognosis for this child with the orbital embryonal tumour, including the surveillance and the late effects to anticipate. (2 marks) [4][5]