A 14-year-old girl with newly diagnosed osteosarcoma of the proximal humerus has completed 10 weeks of neoadjuvant chemotherapy (doxorubicin, cisplatin, methotrexate). Repeat MRI shows a 40% reduction in tumor size. The patient is now scheduled for surgery. What is the most appropriate next step?

Explanation

## Clinical Context This patient has completed standard neoadjuvant chemotherapy with radiological evidence of response (40% size reduction). Before proceeding to definitive surgery, a critical safety check is needed. ## Correct Answer: Repeat Chest CT Before Surgery **Key Point:** Repeat chest CT is mandatory before surgical resection to: 1. Detect new or progressive pulmonary metastases that would change treatment intent 2. Assess resectability of any lung lesions 3. Confirm that the patient remains a surgical candidate ### Why This Timing? **High-Yield:** Pulmonary metastases develop in ~20% of patients at diagnosis and in an additional ~10–15% during neoadjuvant chemotherapy. A repeat chest CT after chemotherapy completion is standard of care because: - It determines whether surgery is curative (resectable disease) or palliative - New metastases may necessitate a change in surgical strategy (e.g., combined limb surgery + pulmonary resection) - It serves as a baseline for post-operative surveillance **Clinical Pearl:** The presence of resectable pulmonary metastases does NOT contraindicate primary tumor resection; both primary and metastatic disease should be resected when feasible. ## Treatment Sequence for Osteosarcoma ```mermaid flowchart TD A[Diagnosis + Staging]:::outcome --> B[Neoadjuvant Chemotherapy<br/>10-12 weeks]:::action B --> C[Repeat Chest CT]:::decision C -->|No new mets| D[Surgical Resection<br/>Primary + any resectable mets]:::action C -->|New unresectable mets| E[Palliative approach/<br/>Consider clinical trial]:::outcome D --> F[Adjuvant Chemotherapy<br/>10-12 weeks]:::action F --> G[Surveillance]:::action ``` **Mnemonic:** **SCARS** — **S**taging, **C**hemotherapy, **A**ssess (repeat imaging), **R**esection, **S**urvey ## Why Not the Other Options? - **Option A (Direct surgery):** Omits critical pre-operative staging; misses ~10–15% of patients who develop metastases during chemotherapy. - **Option B (More chemotherapy):** Standard neoadjuvant duration is 10–12 weeks. Extending without evidence of inadequate response is not indicated and delays definitive surgery. - **Option C (Repeat biopsy):** Unnecessary; radiological response (40% size reduction) is sufficient to proceed. Repeat biopsy adds morbidity without changing management. ## Citation [cite:Robbins 10e Ch 26], [cite:Orthopaedic Surgery: Principles and Practice 6e Ch Bone Tumors]