Abstract
Background: The population of cancer patients with second primary malignancies (SPMs) is rapidly growing. The relationship between radiotherapy and SPMs for some types of tumors is unknown or debated. Methods: We identified 24 types of first primary malignancies (FPMs) between 2004 and 2015 in the Surveillance, Epidemiology, and End Results (SEER) database. Patients in the radiotherapy group were matched to those in the no radiotherapy group with a matching ratio of 1:1. After propensity-score matching (PSM), additional competing risk regression analyses was performed to calculate the efficacy of radiotherapy to SPMs in the PSM-adjusted population. In addition, the Fine & Gray model was utilized in the primary cohorts and stratified analyses were performed based on surgery. Results: This study included a total of 2,831,789 eligible patients with tumors diagnosed from 2004 to 2015 in the SEER 18 database, amongst whom 100,194 (3.5%) patients developed SPMs. We have observed higher risks of SPMs associated with radiotherapy in several types of tumors in the PSM-adjusted populations. Basically, the results in the PSM-adjusted populations were consistent with outcomes in the multivariable competing risk models. Meanwhile, in subgroup analyses stratified by surgery, some other types of tumor (except for those with positive results in the PSM-adjusted cohorts) with radiotherapy were also associated with higher prevalence of SPMs in the subgroups of surgical treatment. Conclusions: We present a comprehensive and newest pan-cancer study illustrating the effect of radiotherapy on the incidence of SPMs. The findings merits further investigation and may ultimately impact treatment decision-making for tumor management. Funding: None. Competing Interest Declaration: The authors declare that they have no competing interests. Ethics: This study is in accordance with the Declaration of Helsinki and has been approved by the Institutional Review Board at the West China Hospital.
Highlights
Radiotherapy remains one of the major treatment modalities for cancers
This study enrolled a total of 2,831,789 patients meeting the inclusion criteria with tumors diagnosed from 2004 to 2015 in the SEER 18 registry, amongst whom 100,194 (3.5%) patients developed a second primary malignancy
We demonstrated a higher risk of secondary primary malignancies (SPMs) of patients with small cell lung carcinoma and small bowel adenocarcinoma after radiotherapy
Summary
Radiotherapy remains one of the major treatment modalities for cancers. More than 50% of all cancer patients need radiotherapy at some point in the treatment process [1]. Gonzalez et al have performed a comprehensive and representative study related to the impact of radiotherapy on secondary cancers [8] They failed to include all the tumor sites of the prior tumors, and they classified patients by tumor sites instead of pathological types. This study did not utilize competing risk regression models (such as the Fine and Gray model) considering death and secondary malignancies as competing risks. They did not include patients after 2002, and some radiotherapy techniques, such as intensity-modulated radiotherapy (IMRT), have not been commonly used at that time [17]
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