Primary Tumor Radiotherapy During EGFR-TKI Disease Control Improves Survival of Treatment Naïve Advanced EGFR-Mutant Lung Adenocarcinoma Patients.

Background Whether radiotherapy only for primary lung tumor (RTPLT) after epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) therapy improves survival of treatment naive advanced EGFR-mutant lung adenocarcinoma (LAD) patients with/without polymetastasis. Materials and Methods This was a retrospective, single-center, observational study. Patients with stage IIIB-IV EGFR-mutant LAD with disease control by EGFR-TKI therapy were divided into curative RTPLT, and control, without radiotherapy (WRTPLT) groups. Results A total of 138 patients were enrolled; 46 in the RTPLT group and 92 in the WRTPLT group. Amongst them, 37% had oligometastasis, and 26.1% brain metastasis. The RTPLT group had both significantly longer progression-free survival (PFS) (27.5 months [95% CI 18.1-36.9] vs 10.9 months [95% CI 6.3-15.5], P<0.001) and overall survivor (OS) (NR [95% CI NR-NR] vs 38.0 months [95% CI 31.2-44.8], P<0.001), respectively, when compared to the WRTPLT group. In multivariate analysis, the adjusted HR of radiotherapy on PFS was 0.30 (0.19-0.47) and on OS, 0.11 (0.04-0.30). Patients with oligometastasis had significantly longer PFS than those with polymetastasis with an HR of 0.35 (0.14-0.85), P=0.02. Patients with either oligometastasis or polymetastasis had significant longer PFS when undergoing radiotherapy than those without (both P<0.05). An EGFR-TKI to radiotherapy interval <24 weeks seemed more beneficial (P=0.097). Radiation pneumonitis comprised 32 (69.6%), 12 (26.1%), and two (4.3%) cases of common terminology criteria grade I, II, and III, respectively. Conclusion Curative RTPLT can prolong survival in patients with LAD following EGFR-TKI disease control, both involving oligometastasis and polymetastasis. RTPLT within 24 weeks after EGFR-TKI initiation appeared to be more beneficial with tolerable radiation pneumonitis.