Case Report
A 24-year-old woman presented with a 2-year history of a painless limp on the left side requiring a walking stick to mobilise. Her medical history included keratoconus associated with diabetes mellitus and anxiety disorders, treated by Metformin (850 mg), Vildagliptin/Metformin (50 mg/1000mg), and Fluoxetine (20 mg), respectively. The patient denied any history of pain, loss of weight-appetite, fever, or family history of cancer.
Radiological examination was conducted with hip X-ray revealed a large aggressive tumour of the left hemipelvis. The tumour involved entirety of acetabulum and extended to the sacroiliac joint. (Figure 1 ).
Magnetic resonance imaging (MRI) showed an extensive bone forming tumour involving whole hemipelvis and eroding the hip (Figure 2 ). There were no lung metastases. The patient underwent an open biopsy through the ilioinguinal approach, and the diagnosis of a giant cell rich telangiectatic osteosarcoma was made by the specialist sarcoma pathology team.
The interdisciplinary sarcoma group recommended neoadjuvant chemotherapy; MAP (methotrexate, doxorubicin, cisplatin) regimen was given to the patient. The MAP regimen consisted of 120 mg/m2, doxorubicin 37ยท5 mg/m2 per day on days 1 and 2 (on weeks 1 and 6) followed 3 weeks later by high-dose methotrexate 12 g/m2 over 4 hours.
Sequential computed tomography (CT) indicated that the tumour did not respond to chemotherapy and the tumour had increase in size, involving the entire of the hemipelvis, the hip joint and crossed the sacroiliac joint (Figure 3 ). External hemipelvectomy (left hindquarter amputation) was performed in this case. Post-surgery, the patient received adjuvant chemotherapy MAP (methotrexate, doxorubicin, cisplatin) + Mifamurtide.
Histopathological examination of the resected specimen showed a large malignant bone forming tumour, 20 cm x 25 cm x 16 cm, which partly destroyed the ilium and widely invaded adjacent soft tissues (Figure 4 ). The tumour surrounded the acetabulum, but did not breach the articular surface, there was no involvement of the hip joint or femur.
The tumour was relatively well circumscribed and mostly composed of large cyst-like blood filled spaces lined by markedly pleomorphic tumour cells and a small amount of bone and osteoid formation. Abundant osteoclast-like giant cells permeated the tumour and septa (Figure 5 ). The femur showed evidence of osteopenia.