Clinical evaluation of potential usefulness of serum lactate dehydrogenase level in follow-up of small cell lung cancer

Background: Lactate formation is upregulated in tumor cells by lactate dehydrogenase (LDH). High serum LDH level is linked to many malignancies with poorer survival, but tumor LDH has not been well investigated in small cell lung cancer (SCLC). Patients and Methods: The study was performed in 120 cases of SCLC confirmed by pathological examination. The evaluation of treatment response to chemotherapy was based on response evaluation criteria in solid tumors criteria. The serum LDH levels were determined at diagnosis and follow-up visits. The distribution and differences in LDH change and the chemotherapeutic response rate was evaluated by using chi(2) tests. Receiver operating characteristic curves were calculated to select the cut-off level of an increase in LDH indicating significant progression. The correlation of time of serum LDH normalization, time-to-progression (TTP), and overall survival (OS) were analyzed by Pearson correlation. Influence of increasing LDH on survival was calculated using the Kaplan-Meier method. Results: At diagnosis, significant differences in LDH levels were found between the groups with limited or extensive. In contrast to the limited-stage group, the extensive-stage group showed significantly decreased the level of LDH after the first-line chemotherapy. In patients whose diseases progressed, LDH levels were significantly higher in the last 1-month period preceding progression compared with the level at the progression. In the follow-up, we found that prolonging periods of serum LDH normalization were co-related to TTP and OS significantly. An increase in LDH by at least 51.5 U/L was found to be associated to a significantly higher probability of disease progression, and patients with initial increased LDH had a significantly reduced probability of survival. Conclusions: LDH is validated for its potential usefulness as markers for monitoring treatment response in SCLC and also suitable for discriminating between disease and disease-free periods.