Prognostic significance of serum lactate dehydrogenase in osteosarcoma of the extremity: experience at Rizzoli on 1421 patients treated over the last 30 years. The study evaluated the correlation between pretreatment serum lactate dehydrogenase (LDH) levels with the stage of disease and its clinical prognostic value.Pretreatment serum LDH of 1421 patients with osteosarcoma of the extremity were assessed to investigate whether the enzyme correlates with the stage of the tumor. In 860 assessable patients with localized disease, treated according to 10 different protocols of adjuvant (four) and neoadjuvant chemotherapy (six), we also evaluated the correlation between the serum levels of LDH and outcome.According to the stage of disease, the rate of high serum level of LDH was significantly higher in 199 patients with metastatic disease at presentation than in 1222 patients with localized disease (36.6% vs 18.8%; P < 0.0001). In these patients, the 5-year disease-free survival was 39.5% for patients with high LDH levels and 60% for those with normal values. The 5-year disease-free survival correlated with serum level of LDH at univariate and multivariate analysis, although it lost its significance when histologic response to chemotherapy was also considered in the multivarite analysis.Serum LDH has a prognostic value and it should be considered in evaluating the results of therapeutic trials of chemotherapy, as well as defining a category of patients at high-risk of relapse to be treated with a more aggressive regimen.