Impact of early tumor reduction on outcome differs by histological subtype in stage III non-small-cell lung cancer treated with definitive radiotherapy

We retrospectively investigated the impact on survival of early tumor reduction during definitive radiotherapy for inoperable stage III non-small cell lung cancer (NSCLC) patients, according to their histological subtypes. Between November 2006 and December 2012, 152 consecutive patients with inoperable stage III NSCLC who underwent definitive radiotherapy were reviewed retrospectively. Forty-one patients were excluded for not satisfying the inclusion criteria. Forty-five (40.5 %) and 48 (43.2 %) patients were diagnosed with squamous cell carcinoma (SQC) and adenocarcinoma (ADC), respectively. The tumor reduction rate (TRR) was defined as follows: TRR = 1-[gross tumor volume (GTV) on computed tomography at shrinking irradiation field planning]/(GTV on computed tomography at the initial treatment planning). The Cox proportional hazard model was used to identify significant prognostic factors for overall survival (OS) and progression-free survival (PFS). We evaluated 111 patients, with a median follow-up time of 52.2 months in surviving patients. The median TRR was 45.9 %. In all patients, there were significant associations between TRR and PFS (P = 0.036) on multivariate analysis, although TRR had no correlation with OS (P = 0.141). With respect to histological subtype, multivariate analyses revealed that a higher TRR showed significant associations with better OS and PFS in the SQC group (P = 0.013 and 0.040, respectively). In contrast, a higher TRR was associated with poorer OS in the ADC group (P = 0.030); there was no association between TRR and PFS. We found that a higher TRR is a promising prognostic factor for better survival and disease control in SQC patients.