Ewing sarcoma (ES) and Osteosarcoma (OS) are the 2 most common malignant primary bone tumors. A patient's response to neoadjuvant chemotherapy has important implications in subsequent patient management and prognosis, as a favourable response to chemotherapy allows orthopedic oncologists to be more aggressive in pursuing limb-sparing surgery. An accurate and non-invasive pre-operative marker of response would be ideal for planning surgical margins and as a prognostic tool.

ES and OS have differing biological characterisitcs and respond differently to chemotherapy. We reviewed 18F-FDG PET imaging characteristics of ES and OS patients at baseline and following treatment to determine whether this biological variation is reflected in their imaging phenotype. A retrospective review of ES and OS patients treated with neoadjuvant chemotherapy and surgery was done, correlating PET results with histologic response to chemotherapy.

Change in the maximum standardized Uptake Value (SUVmax) between baseline and post-treatment scanning was not significantly associated with histologic response for either ES or OS. Metabolic tumor volume (MTV) and the percentage of injected 18F-FDG dose (%ID) in the primary tumor were found to be different for ES and OS response subgroups. A 50% reduction in MTV (MTV2:1 < 0.5) was found to be significantly associated with histologic response in OS. Using the same criteria for ES incorrectly predicted good responders. Increasing the cut-offs for ES to a 90% reduction in MTV (MTV 2:1 < 0.1) resulted in association with histologic response.

Response to neoadjuvant chemotherapy as reflected by changes in PET characteristics should be interpreted differently for ES and OS.

Purpose

Ewings Sarcoma (ES) and Osteosarcoma (OS) behave and respond differently to chemotherapy and any interpretation of diagnostics tests to predict a patients response to treatment must consider this. We reviewed 18F-FDG PET imaging characteristics of consecutive series of ES and OS patients to determine if any differences in PET imaging existed between them.

Introduction The aim of this study was to assess the accuracy of CT-guided core needle biopsy of musculo-skeletal tumours.

Methods This is a retrospective study on a series of 127 patients with a musculoskeletal tumours. The biopsies were performed over a four year period from 1998 to 2001. The accuracy of the CT-guided core needle biopsy was determined by comparing the histology of the biopsy with the final histology of the specimen obtained at open biopsy or surgical resection of the tumour. The effective accuracy was determined by the accuracy of the biopsy to diagnose benign versus malignant.

Results CT-guided core needle biopsy in this series has an overall accuracy of 80%. The effective accuracy as determined by a malignant versus benign lesion was 89%. There were 86 malignant tumours with a biopsy accuracy of 81% and there were 41 benign tumours with a biopsy accuracy of 78%. The positive predictive value (PPV) of a malignant tumour is 100% and the PPV of benign tumour 94.9%. The most common site of biopsy was from the femur and thigh, together accounting for 39.4% of the tumours. The most common tumours in this series were liposarcoma (n=12), osteosarcoma (n=11) and giant cell tumour (n=11). There were no reported complications arising from the biopsy.

Conclusions CT-guided core needle biopsy is a safe and effective procedure that is important in the diagnosis and management of musculoskeletal tumours.