Results:
A 13-year-old girl without relevant medical antecedents presented with a 4-week history of worsening pain, swelling and loss of strength in her left upper limb. Plain radiography showed an osteolytic lesion involving the proximal humerus, and magnetic resonance imaging (MRI) revealed a bone lesion with characteristics of aggressiveness and associated soft tissue mass (Fig. 1a and b). Trucut biopsy showed a heterogeneous neoplastic proliferation with round cell nests on a collagen stroma and osteoid foci, compatible with conventional osteosarcoma. The bone scan and thoracic computed tomography (CT) ruled out distant metastases but revealed two left axillary and supraclavicular nodular lesions of 17 and 21 mm, respectively (Fig. 1c). An axillary lymph node biopsy was compatible with metastasis of osteosarcoma.
The patient started chemotherapy treatment according to Spanish Society of Pediatric Hematology and Oncology protocol for localized osteosarcoma (SEHOP 2010) (based on methotrexate, cisplatin, doxorubicin, and ifosfamide) presenting a significant decrease in swelling, pain and normalization of analytical parameters in the first weeks of treatment. During induction chemotherapy she suffered from a spontaneous pathological fracture. On week 11 she developed local swelling, pain and increased levels of LDH (lactate dehydrogenase) and alkaline phosphatase. The evaluation carried out on week 12, prior to the loco-regional surgical treatment, showed signs of local progression with increase of the soft tissue mass, increased diaphyseal extension and full infiltration of the epiphysis. Local lymph nodes showed radiological stability. The extension work-up ruled out metastatic progression. The patient underwent upper limb amputation and lymph node dissection, since limb sparing surgery was deemed unlikely to achieve optimal local control after discussion in our local multidisciplinary tumour board. The surgical specimen showed a neoplastic proliferation with 30% post-chemotherapy necrosis and free surgical margins (R0 Ennekin). Atypical cells with epithelioid and focal rhabdoid habit were observed, with positivity for myogenin and desmin. In other areas there were foci of cartilage and fine osteoid (Fig. 2). The neoplasm was reclassified as an osteosarcoma with a focal component of rhabdomyosarcoma. Among the multiple lymph nodes resected, only two of them showed neoplastic infiltration with similar characteristics to those described at bone specimen.
PET-CT performed three weeks after surgery showed new cervical adenopathies, multiple bilateral pulmonary nodules and bone lesions compatible with metastatic progression. She received two cycles of the VIT regimen [vincristine (1.5 mg / m2 / day, days +1 and +8), irinotecan (50 mg / m2 / day x 5 days) and temozolomide (150 mg / m2 / day x 5 days)] in a 21-day interval. She progressed after these two cycles and ultimately died of disease progression.
An extensive molecular analysis was performed on surgical material at progression, including tumour whole exome sequencing (WES), RNA sequencing and methylation profiling. It revealed 21 homologous recombination defects that resulted in a high genomic rearrangement but with a low mutational burden. Mutational disruption ofTSC2 (stop-gain mutation), TP53 (stop-gain mutation),CCNE1 (focal duplication and mRNA overexpression) andSETD2 (missense mutation) were revealed. A DNA Methylation-Based Classifier for sarcomas was inconclusive. This analysis was only available after the patient passed away and could not be used for therapeutic purposes.