The purpose of this study was to investigate the failure patterns of three-dimensional radiotherapy of primary tumours combined with first-line systemic therapy and the influence of radiotherapy-related factors for stage IV non-small cell lung cancer.

Seven hundred and forty-eight cases with the initial diagnosis of stage IV non-small cell lung cancer that met the inclusion criteria were selected from 1509 cases registered from March 2003 to July 2021 for univariate analysis and failure patterns test using the chi-square test. Kaplan-Meier survival analysis was performed with the log-rank test and Cox regression model for multifactor prognostic analysis. A value of P below 0.05 indicated a statistically significant difference.

The failure incidence of first-line treatment was 72.3 % in 748 cases and 33.6 % within 6months, 38.8 % between 6 and 12months, 19.4 % between 12 and 24months and 8.1 % after 24months. A significant difference was observed in the median survival time, which was 7.2, 13.4, 22.2, and 37.6months (χ²=324.580, p<0.000), respectively. The incidence of recurrent failure was 20.4 %. A decrease was observed in the recurrence rate with the increasing dose of radiotherapy to the primary tumour, and no significant difference in the incidence of recurrent failure was observed between oligometastatic and non-oligometastatic tumours. The incidence of metastatic failure was 89.4 %, with the order of incidence as follows (from highest to lowest): brain, bone, lung, liver, pleural cavity, distant lymph nodes, adrenal gland, other body parts. The incidence of additional metastases was approximately 50 %, and the progression of synchronous metastases concerned approximately one third of the cases. The metastatic status, time of treatment failure, pathology type, gender, and at least 63Gy during the same period of four to six cycles of chemotherapy were independent factors in the prediction of prognosis.

The failure patterns of radiotherapy for primary tumours in stage IV non-small cell lung cancer was different from that of first-line systemic therapy alone, with significantly lower local failure, predominant metastatic failure, and the highest incidence of brain metastases. The later treatment failure occurs, the longer will be the oligometastatic status. Oligometastatic cancer, female sex, non-squamous cell carcinoma, the late occurrence of treatment failure, and at least 63Gy concurrent four to six cycles of chemotherapy were independent prognostic factors for prolonged survival.