Abstract
Our study aims to estimate the incidence of metachronous second primary lung cancer(SPLC) in initial primary lung cancer(IPLC) survivors and to determine whether radiotherapy affects the risk of metachronous SPLC in the first five years after the diagnosis of lung cancer. Incidence data of IPLC individuals who survived ≥2 years were obtained from SEER-18 database in 2004–2007. Joinpoint regression analysis and competing risk analysis were used to calculate the incidence of metachronous SPLC. Propensity score matching and decision analysis were available to estimate the effect of radiotherapy on metachronous SPLC. 264 of 11657 IPLC survivors with radiotherapy and 1090 of 24499 IPLC survivors without radiotherapy developed metachronous SPLC during 5-year follow-up, respectively. In joinpoint regression analysis, the 5-year incidence of metachronous SPLC in the radiotherapy group was lower than that in the nonradiotherapy group(2385 per 100,000 vs 4748 per 100,000, HR = 0.43,95% CI:0.39–0.47). Competing risk analysis showed that the survivors with radiotherapy were associated with the lower 5 year incidence of metachronous SPLC compared with those without radiotherapy(2.28% vs 4.47%, HR = 0.49,95% CI:0.43–0.57). Through propensity score matching, 4077 pairs of survivors were available to further study that radiotherapy potentially decreased the risk of developing metachronous SPLC with the adjustment of various factors(2.5% vs 3.3%, HR = 0.72, 95% CI:0.55–0.96). Decision analysis suggested that radiotherapy was a negative independent risk factor of metachronous SPLC with clinical net benefit in a range of risk thresholds (2% to 5%). Survivors of IPLC with radiotherapy likely had a low risk of metachronous SPLC during the first five years follow-up, especially non-small cell lung cancer.
Highlights
Our study aims to estimate the incidence of metachronous second primary lung cancer(SPLC) in initial primary lung cancer(IPLC) survivors and to determine whether radiotherapy affects the risk of metachronous SPLC in the first five years after the diagnosis of lung cancer
The IPLC survivors without radiotherapy seemed to have a higher risk of metachronous SPLC than those with radiotherapy, which were identified in propensity score matching and decision analysis
We found that the presence of metachronous SPLC did not reduce overall survival of IPLC patients, either in the radiotherapy group or in the nonradiotherapy group
Summary
Our study aims to estimate the incidence of metachronous second primary lung cancer(SPLC) in initial primary lung cancer(IPLC) survivors and to determine whether radiotherapy affects the risk of metachronous SPLC in the first five years after the diagnosis of lung cancer. IPLC individuals can be classified as a high-risk population of lung cancer.The present results about the association between radiotherapy and the risk of second primary lung cancer(SPLC) were controversial Tucker and his colleagues[15] claimed that the risk of developing SPLC of the patients with chest radiotherapy was approximately two fold higher than those without chest radiotherapy in small cell lung cancer. Our first aim is to estimate the incidence of developing metachronous SPLC in the individuals with IPLC who received radiotherapy through joinpoint regression analysis and competing risk analysis. The second aim of our study is to determine whether radiotherapy is associated with the incidence of metachronous SPLC in the first five years, which was performed through propensity score matching and decision analysis. According to the accepted diagnostic criterion of Martini and Melamed[18], the patients who were diagnosed as metachronous SPLC need to fulfill the following situations: (1)IPLC and SPLC are reported different histology; (2) When IPLC and SPLC display same histology, the following criteria must be met:(1)the disease-free interval between IPLC and SPLC must be more than 2 years. (2) IPLC and SPLC origin from carcinoma in situ, or occur in different lobes with no metastatic carcinoma of common lymph nodes and no extrapulmonary metastasis at the time of diagnosis
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