Benefits of postoperative thoracic radiotherapy for small cell lung cancer subdivided by lymph node stage: a systematic review and meta-analysis

Background: Whether postoperative thoracic radiotherapy (PORT) is beneficial for small cell lung cancer (SCLC) of different lymph node stages remains uncertain; therefore, the purpose of this meta-analysis was to explore the clinical significance of PORT for SCLC patients subdivided by lymph node status. Methods: The PubMed, OVID, Web of SCI, EMBASE, Google Scholar, Cochrane Library, Chinese National Knowledge Infrastructure and Wanfang databases were systematically searched to identify eligible studies where SCLC patients received PORT based on lymph node stage. The main outcome measures were 1-, 3-and 5-year overall survival (OS) rates, as well as 1-, 2-and 3-year local regional recurrence (LRR) rates. All data were analyzed using STATA 12.0 and expressed as risk ratios (RR) with their corresponding 95% confidence intervals (95% CI). Results: Five cohort studies, including 3,497 SCLC patients (578 receiving PORT and 2,919 not) were included in this study. PORT significantly decreased the 1-, 2-and 3-year LRR rates (RR = 0.14, 0.28 and 0.27, respectively; Pall<0.05), but did not improve the 1-, 3-or 5-year OS rates when all patients were analyzed together. However, subgroup analysis showed that in the pN0 group PORT did not improve the 1-, 3-or 5-year OS rates or decrease the 1-, 2-or 3-year LRR rates; in the pN1 group PORT reduced the 1-, 2-and 3-year LRR rates (RR = 0.11, 0.16 and 0.17, respectively; Pall<0.05) and improved the 1-year OS rate (RR = 0.40; P<0.001), but not the 3-or 5-year OS rates; in the pN2 group PORT significantly reduced the 1-, 2and 3-year LRR rates (RR = 0.14, 0.15 and 0.15 respectively; Pall<0.05) and improved the 1-, 3-and 5-year OS rates (RR = 0.46, 0.72 and 0.85, respectively; Pall<0.05). Conclusions: This is the first meta-analysis of the benefits of PORT for SCLC patients. Although derived from retrospective cohort studies, the data showed that PORT significantly reduced the risk of recurrence and improved survival for patients with pN2-SCLC; however, patients with pN0-SCLC did not benefit from PORT, whereas for patients with pN1-SCLC, PORT reduced the LRR rates and improved the 1-year survival rate. The long-term survival benefits of PORT remain unclear and will require further prospective studies.