The SEER database comprises the initial treatment information. We placed patients with the first primary PBC into two groups: those who received RT and those who did not. The former (RT group) included BC patients who had surgery as well as (neo)adjuvant RT, whereas the latter no RT group included those who underwent surgery without radiotherapy.
The primary outcome of interest was the occurrence of an SEC, defined as a malignancy developing after at least one year of the initial therapy of BC patients. Follow-up ended at the point of interest, death, or the end of follow-up, whichever came first. The secondary outcomes were the overall survival (OS) and cancer-specific survival (CSS) of SECs. The endpoint events of OS and CSS were measured from the time after EC diagnosis. OS included all deaths from any cause during the follow-up period, while patients who were still alive were right-censored. CSS was defined based on the cause of death from esophageal etiology, whereas non-SEC deaths were considered competing risks, and patients alive were right-censored. Here the "non-SEC" developed a second cancer with a different cancer diagnosis.
The primary outcome of interest was the occurrence of an SEC, defined as a malignancy developing after at least one year of the initial therapy of BC patients. Follow-up ended at the point of interest, death, or the end of follow-up, whichever came first. The secondary outcomes were the overall survival (OS) and cancer-specific survival (CSS) of SECs. The endpoint events of OS and CSS were measured from the time after EC diagnosis. OS included all deaths from any cause during the follow-up period, while patients who were still alive were right-censored. CSS was defined based on the cause of death from esophageal etiology, whereas non-SEC deaths were considered competing risks, and patients alive were right-censored. Here the "non-SEC" developed a second cancer with a different cancer diagnosis.
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