br Discussion The presence of metastases at the time of
Discussion The presence of metastases at the time of diagnosis is a significant prognostic factor in osteosarcoma . Skeletal metastases at time of presentations appears to carry a worse prognosis than pulmonary metastases . Furthermore, the chance of survival can be improved by surgical resection of all metastases . Systemic staging and the search for the presence of metastases therefore form an integral part of the initial diagnostic work-up of a patient with osteosarcoma. The aim of this study was to determine the value of pre-treatment serum LDH and ALP in predicting the presence of skeletal or pulmonary metastases in patients with conventional high-grade osteosarcoma of the extremities. Neither serum ALP or LDH was found to be of value as prognostic factors for the presence of pulmonary metastases. In terms of skeletal metastases both serum ALP and LDH were found to be significant. Serum LDH, however, lost its statistical significance in a multivariate model that included tumour volume. Lactate dehydrogenase is known to reflect systemic cancer burden and its prognostic significance has been illustrated in various malignancies, including Ewing\'s sarcoma [17,18]. A recent meta-analysis of studies evaluating the effect of high LDH levels on overall survival found a pooled hazard ratio of 1.92 (95% CI 1.53–2.40) . The Multi-Institutional Osteosarcoma Study (MIOS) found serum LDH to be the single most predictive factor of adverse outcome . At 6 year follow-up of patients diagnosed with osteosarcoma of the extremities, the event-free survival was 41% for patients with elevated LDH levels compared to 69% for the patients who had normal LDH at diagnosis (p<0.001). A study looking specifically at the prognostic value of LDH in patient with osteosarcoma of the extremities, found that patients who presented without metastases and an increased serum LDH level were also far more likely to develop relapse of disease than those with normal LDH values (60% vs 38%, p<0.001) . Plasma bone-specific ALP has been suggested as a reliable tumour marker for osteosarcoma . Multivariate analysis performed by Mialou et al. identified serum ALP levels in excess of 500 IU/L as an independent risk factor for decreased disease-free and overall survival rates . Furthermore, a influenza a virus in ALP levels following chemotherapy has been shown to correlate with improved response to chemotherapy and survival . On the other hand, some authors have found that serum ALP did not have prognostic value in terms of disease outcome . Although pre-treatment LDH and ALP levels have been shown to serve as a reliable indicator of disease-free survival, its value in predicting the presence of metastases at time of diagnosis remains unclear. In their initial series, Bacci et al. found that the percentage of patients with an elevated serum LDH at the time of diagnosis was significantly higher in patients with metastatic disease than those who had localised disease (64% versus 33%, p<0.0001) . In a larger follow-up series from the Rizzoli institute, involving 1421 patients seen over a 30 year period, pollen grains was noted that 18% of patients with localized disease had elevated LDH levels at presentation compared to 36% of patients with metastatic disease (p<0.0001) . Although high LDH levels were able to predict the presence of metastases with a high degree of specificity (0.81), sensitivity was found to be low (0.38). There was however no differentiation made between skeletal and pulmonary metastases in these studies. To the best of our knowledge this is the first report looking specifically at the predictive value of ALP and LDH in detecting skeletal metastases. In our series serum LDH appeared to be predictive for skeletal, but not pulmonary metastases. Serum LDH, with a cut-off value of 849 IU/L, had a sensitivity of 0.88 and specificity of 0.73 as a marker of skeletal metastases. Multivariate logistic regression analysis by Bacci et al. found that only tumour site (femur and humerus), increased alkaline phosphatase (ALP), tumour volume (>150ml) and duration of symptoms (less than 2 months) were significant factors in the prediction of the presence of metastases at time of presentation . Han et al. found an increased incidence of pulmonary metastases in patients with a pre-treatment serum ALP increased more than twice the upper limit of normal (34% vs 12%; p=0.007) . Similarly, the Rizolli group found increased ALP levels in patients with metastases at time of diagnosis (91.5% vs 61.3%; p<0.001) . The authors did not distinguish skeletal from pulmonary metastases at time of presentation in relation the ALP. Furthermore, there was an increased relapse rate in patients who presented with localized disease and increased ALP levels (55.1% vs 26.4%; p<0.001). The authors noted however that there was no difference in the site of first metastases related to value of the ALP level. Our findings suggest that normal serum ALP levels may be predictive of the absence of skeletal metastases at the time of diagnosis. With a cut-off of 76 IU/L a sensitivity of 100% was reached. Serum ALP remained a significant predictor in a multivariate model that included the pre-treatment tumour volume, with an odds ratio of 9.8 (p=0.02) for skeletal metastases if pre-treatment ALP ≥280 IU/L.