Serum lactate dehydrogenase predicts brain metastasis and survival in limited-stage small cell lung cancer patients treated with thoracic radiotherapy and prophylactic cranial irradiation

Small cell lung cancer (SCLC) is characterized by a high risk of brain metastasis and poor survival. This study aims to assess the prognostic role of lactate dehydrogenase (LDH) in limited-stage small cell lung cancer (LS-SCLC) treated with thoracic radiotherapy (TRT) and prophylactic cranial irradiation (PCI).This study retrospectively evaluated 197 consecutive patients who underwent TRT and PCI for LS-SCLC between November 2005 and October 2017. Both pretreatment and maximal serum LDH levels (mLDH) during treatment were checked, and an increased LDH level was defined as more than 240 IU/ml. Clinical factors were tested for associations with intracranial progression-free survival (IPFS) and overall survival (OS) after PCI. The Kaplan-Meier method was used to calculate survival rates, and multivariate Cox regression analyses were carried out to identify variables associated with survival.Of the total patients, 28 had higher pretreatment LDH levels and mLDH levels were increased in 95 patients during treatment. In patients in the normal and elevated mLDH groups, the 1‑, 2‑, and 5‑year IPFS rates were 96.7% vs. 90.1%, 91.7% vs. 73.8%, and 87.8% vs. 61.0% (P < 0.01), respectively. Compared to those with normal LDH levels, patients with increased mLDH levels had a higher cumulative risk of intracranial metastasis (hazard ratio [HR] 3.87; 95% confidence interval [CI] 1.73-8.63; P < 0.01) and worse overall survival (HR 2.59; 95% CI 1.67-4.04; P < 0.01). The factors LDH level at baseline or changes between pretreatment level and maximum level during treatment failed to predict brain metastases or OS with statistical significance. In the multivariate analyses, both mLDH during treatment (HR 3.53; 95% CI 1.57-7.92; P = 0.002) and patient age ≥ 60 (HR 2.46; 95% CI 1.22-4.94; P = 0.012) were independently associated with worse IPFS. Factors significantly associated with worse OS included mLDH during treatment (HR 2.45; 95% CI 1.56-3.86; P < 0.001), IIIB stage (HR 1.75; 95% CI 1.06-2.88; P = 0.029), and conventional radiotherapy applied in TRT (HR 1.66; 95% CI 1.04-2.65; P = 0.034).The mLDH level during treatment predicts brain metastasis and survival in LS-SCLC patients treated with TRT and PCI, which may provide valuable information for identifying patients with poor survival outcomes and possible candidates for treatment intensification.