Osteosarcoma

Diagnosis

Osteosarcoma

History

Ten year-old boy with a painful leg mass.

Findings

Large right distal femoral mass showing intense uptake (SUV max 17.9). The metabolic activity is more pronounced in the periphery of the mass. This lesion is centered on the distal diaphyso-metaphyseal junction and shows large soft tissue component. The right distal femoral physis is not clearly visualized and there is probable tumor extension in epiphysis. On the low-dose CT, there is an aggressive periosteal reaction and osteoid matrix in the medullar cavity.

No other suspicious lesion.

DDx

Osteosarcoma

Ewing’s sarcoma

Lymphoma

Discussion

Osteosarcoma (OS) is the most common primary bone malignancy. It is a mesenchymal tumor in origin, in which  malignant cells can produce osteoid. The epidemiology of OS follows a bimodal distribution with a peak in adolescence and young adulthood and a second peak near the 6th decade of life.

OS is most commonly located in long bones around the knee and has a predilection to arise from the metaphysis. Other primary sites include proximal humerus, pelvis, jaw, fibula and ribs.

Approximately 20% of patients have metastasis at the time of diagnosis; lungs being the most common site followed by bone. Skip metastasis are considered localized disease if skip lesions can be included in surgical resection.

Pretreatment prognostic factors include primary tumor site, size of tumor and metastatic disease. Axial primary tumors have worse prognosis given the more difficult complete surgical resection. After preoperative chemotherapy and surgery, the degree of tumor necrosis seen through histopathological findings is known as a prognostic factor. Patients with at least 90% of tumor necrosis in the primary tumor have better prognosis (good histological response).

Roles of PET/CT FDG

Two recent studies (Byun et al. and Hurley et al.) investigated the performance of PET/CT FDG and bone scintigraphy (BS) for the detection of bone metastasis. Byun et al. concluded a better sensitivity and accuracy of PET/CT FDG compared to BS. However, combination of PET/CT FDG and BS was better than PET/CT FDG alone. Hurley et al. also found that PET/CT FDG was superior than BS, but there was no statistical difference between PET/CT FDG alone and the combination of both modalities. Therefore, they conclude that PET/CT FDG may be able to replace BS.

As the degree of tumor necrosis after neoadjuvant chemotherapy is known as a prognostic factor, some authors investigated PET/CT FDG as a non-invasive method to predict tumor necrosis. Cheon et al. found that a SUVmax < 2 after neoadjuvant chemotherapy was associated with a good histological response and SUVmax > 5 was associated with a poor histologic response. Other authors used SUVmax < 2.5 (Hamada et al.) and > 5 (Kong et al.) after neoadjuvant chemotherapy as a predictor of good and poor histological response respectively. A meta-analysis (Hongtao et al.) also found that SUVmax < 2.5 after neoadjuvant chemotherapy was a valuable predictor of good histological response. Furthermore, they showed that the ratio of SUVmax after chemotherapy/SUVmax before chemotherapy (SUV2/SUV1) < 0.5 was another predictor of good histological response.

References

Cheon et al. : Prediction model of chemotherapy response in osteosarcoma by 18F-FDG PET and MRI. J Nucl Med. 2009 Sep;50(9):1435-40

Costelloe et al. : 18F-FDG PET/CT as an indicator of progression-free and overall survival in osteosarcoma. J Nucl Med. 2009 Mar;50(3):340-7

Hamada et al. : Evaluation of chemotherapy response in osteosarcoma with FDG-PET. Ann Nucl Med. 2009 Jan;23(1):89-95

Bajpai et al. : Prediction of chemotherapy response by PET-CT in osteosarcoma: correlation with histologic necrosis. J Pediatr Hematol Oncol. 2011 Oct;33(7):e271-8

Hongtao et al. : 18F-FDG positron emission tomography for the assessment of histological response to neoadjuvant chemotherapy in osteosarcomas: a meta-analysis. Surg Oncol. 2012 Dec;21(4):e165-70

Byun et al. : Combination of 18F-FDG PET/CT and diffusion-weighted MR imaging as a predictor of histologic response to neoadjuvant chemotherapy: preliminary results in osteosarcoma. J Nucl Med. 2013 Jul;54(7):1053-9

Kong et al. : 18F-FDG PET SUVmax as an indicator of histopathologic response after neoadjuvant chemotherapy in extremity osteosarcoma. Eur J Nucl Med Mol Imaging. 2013 May;40(5):728-36

Byun et al. : Comparison of (18)F-FDG PET/CT and (99 m)Tc-MDP bone scintigraphy for detection of bone metastasis in osteosarcoma. Skeletal Radiol. 2013 Dec;42(12):1673-81

Hurley et al. : Comparison of (18) F-FDG-PET-CT and Bone Scintigraphy for Evaluation of Osseous Metastases in Newly Diagnosed and Recurrent Osteosarcoma. Pediatr Blood Cancer. 2016 Aug;63(8):1381-6

HaDuong et al. : Sarcomas. Pediatr Clin North Am. 2015 Feb;62(1):179-200

Geller et al. : Osteosarcoma: a review of diagnosis, management, and treatment strategies. Clin Adv Hematol Oncol. 2010 Oct;8(10):705-18

Osteosarcoma and Malignant Fibrous Histiocytoma of Bone Treatment (PDQ®): Health Professional Version. PDQ Cancer Information Summaries [Internet]. Bethesda (MD): National Cancer Institute (US); 2002-2016 Aug 10