Working Diagnosis:
Chondroblastic Osteosarcoma of pelvis with metastasis to spine and lungs

Treatment:
Patient underwent five cycles of etoposide and ifosfamide. Her CT. chest and MRI pelvis and spine two years post-diagnosis showed progression of disease with increased metastatic disease of lungs and lumbar spine. She was started on gemcitabine and docetaxel and also received radiotherapy to the chest and pelvis.

Outcome:
Unfortunately, she further developed new brain metastases and passed away from complications related to diffuse leptomeningeal carcinomatosis.

Author's Comments:
Osteosarcoma is the most common primary bone tumor with peak incidence occurring between the ages of 10-30 years old. chondroblastic osteosarcoma (COS) has shown a poor response to chemotherapy and a high rate of metastasis. In dancers, right-groin pain can be misdiagnosed as musculoskeletal strain. This is a unique case as her initial hip films were normal and her cancer was found on subsequent MRI for further evaluation. While COS are reported, we are not aware of any case reports that have presented in this manner. It is crucial to keep this diagnosis in the differential when examining a case of hip pain in an adolescent that is out of proportion to what is expected for a muscular strain.

Editor's Comments:
Increasing treatment modalities for cancer has led to a rise in cancer remission rates. Patients returning to sporting activities should have detailed education regarding how their cancer treatments may impact their physiology and return to sport. For example, chemotherapies utilizing platinum agents have a higher risk of peripheral neuropathy effecting their proprioception. As a result, there is a higher risk of ankle inversion injuries as the patient returns to sports.

Leptomeningeal carcinomatosis is metastatic spread of a cancer to the pia and arachnoid matter of the brain. It is an uncommon and often late complication seen in 5-8% of solid tumor cases and 5-15% of hematological cancers. Despite advancing and multimodal treatments, it currently heralds a rapid decline in patient health. Definitive diagnosis is often due to malignant cells being found in the cerebrospinal fluid or leptomeningeal enhancement on brain MRI.

References:
1. Aggerholm-Pedersen N, Maretty-Nielsen K, Baerentzen S, et al. Chondrosarcoma: the impact of comorbidity - 30 years of experience from a population-based database including 199 consecutive chondrosarcoma patients. Orthopedic research and reviews. 2019; 11: p.109-116. doi: 10.2147/ORR.S205953
2. Blank AT, Wakefield C, Khalighi M, Jones KB, Randall RL. Epithelioid Osteoblastoma of the Proximal Femur in a 19-Year-Old Female: A Case Report and Review of Literature. J Orthop Case Rep. 2019;9(5):74-77. doi: 10.13107/jocr.2250-0685.1542.
3. Mayo, J. Chondroblastic osteogenic sarcoma of the humerus. Med J Aust. 1948 Aug 7;2(6):153-5. doi: 10.5694/j.1326-5377.1948.tb78263.x.
4. Stark A, Aparisi T, Ericsson JL. Human osteogenic sarcoma: fine structure of the chondroblastic type. Ultrastruct Pathol. 1984;6(1):51-67. Doi: 10.3109/01913128409016665.
5. Tsagozis P, Laitinen MK, Stevenson JD, Jeys LM, Abudu A, Parry MC. Treatment outcome of patients with chondroblastic osteosarcoma of the limbs and pelvis. Bone Joint J. 2019 Jun;101-B(6):739-744. doi: 10.1302/0301-620X.101B6.BJJ-2018-1090.R1.

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