Prognosis of severe lymphopenia after postoperative radiotherapy in non-small cell lung cancer: Results of a long-term follow up study.

PURPOSE

To investigate the incidence and prognosis of severe radiation-induced lymphopenia (sRIL) after postoperative radiotherapy (PORT) for resected NSCLC.

PATIENTS AND METHODS

Between 1998 and 2017, 170 patients treated with PORT for NSCLC were retrospectively reviewed. Lymphopenia was divided into tertiles with severe lymphopenia defined as absolute lymphocyte counts (ALC) < 0.37 × 10/ul.

RESULTS

sRIL was observed in 32.3% of patients. Multivariable logistic regression analysis indicated sRIL was associated with planning target volume radiation fraction numbers (OR 1.09,  = 0.005) and total lung mean dose (OR 1.12,  = 0.006). With a median follow-up time of 12.2 years, the median progression-free survival and overall survival were 14.8 months and 28.4 months respectively in patients with sRIL, vs. 21.7 months ( = 0.008) and 48.3 months ( = 0.01) respectively in patients without sRIL. Multivariable analyses indicated sRIL significantly decreased OS (HR 1.95,  < 0.01). Since PORT for stage I-II NSCLC was done largely for positive margins, which may confound the contribution of severe RIL, we analyzed stage III separately and found that sRIL also significantly decreased OS (HR 1.88,  = 0.004) in multivariable analysis.

CONCLUSION

For this long-term outcome study, severe RIL correlated with total lung mean dose and radiation fractionation numbers, and was a strong prognostic factor for poor survival in PORT patients, particularly in patients with stage III NSCLC, highlighting the importance of an intact immune system for post-radiation immunologic disease surveillance.