The effect of non-small cell lung cancer histology on survival as measured by the graded prognostic assessment in patients with brain metastases treated by hypofractionated stereotactic radiotherapy

BACKGROUND: The purpose of this study was to investigate the impact of histology on survival stratified by the Graded Prognostic Assessment (GPA) for non-small cell lung cancer (NSCLC) in a group of selected patients treated recently. METHODS: A total of 171 NSCLC patients with brain metastases treated by hypofractionated stereotactic radiotherapy with or without whole-brain radiotherapy between 2001 and 2011 were included. The GPA score was calculated for each patient. Tumor histologies were categorized into adenocarcinoma (ADCA) and non-ADCA. Median survival time (MST, in months) was calculated using the Kaplan-Meier method. The log-rank test was used to determine statistical differences. RESULTS: MSTs by histology were: ADCA 15 (n = 92) and non-ADCA 10 (n = 79) (p < 0.001). For all patients, the MSTs by GPA score were: GPA 3.5-4, 24; GPA 2.5-3, 15; GPA 1.5-2, 9 and GPA 0-1, 6 (p < 0.001). The histology of ADCA showed a statistically significant higher MST than non-ADCA for patients with GPA 2.5-4. For GPA 2.5-3, MSTs were: ADCA 18, non-ADCA 10 (p = 0.007); for GPA 3.5-4, MSTs were: ADCA 30, non-ADCA 17 (p = 0.046). For GPA 0-2, MSTs did not differ significantly by histology. For GPA 0-1, MSTs were: ADCA 8, non-ADCA 4 (p = 0.146); GPA 1.5-2, MSTs were: ADCA 10, non-ADCA 8 (p = 0.291). We further found that non-ADCA in upper GPA class (3.5–4) had similar survival with ADCA in lower GPA class (2.5–3) (MSTs were 17 and 18, respectively, p = 0.775). This phenomenon also happened between patients of non-ADCA in upper GPA class (2.5–3) and those of ADCA in lower GPA class (1.5–2) (MSTs were both 10, p = 0.724). CONCLUSIONS: We confirmed that the histology of NSCLC had effect on the GPA in these selected patients treated recently. ADCA showed a statistically significant higher MST than non-ADCA with GPA 2.5-4. The non-ADCA in upper GPA classes (3.5-4 and 2.5-3) had similar survival to ADCA in lower GPA classes (2.5-3 and 1.5-2, respectively). The histology as a new factor should be added to the original GPA for NSCLC.