Breast cancer is the fifth leading cause of cancer death globally. In this retrospective study, we investigated the effects of the diagnosis-to-first-treatment interval (DFTI) and other related factors on cancer-specific survival in patients with breast cancer. We included 49,426 patients newly diagnosed as having breast cancer during 2011-2017. The Cox proportional hazards model was used to analyze the hazard ratio (HR) for mortality with various DFTIs; the HRs of the 31-60-, 61-90-, and ≥ 91-day DFTI groups did not differ significantly compared with the reference group (DFTI ≤ 30 days). After stratifying the patients according to initial tumor stage and age, we found that patients aged 55-64 and ≥ 65 years with stage II breast cancer treated ≥ 91 days after diagnosis had a 3.34- and 2.93-fold higher mortality risk (95% confidence intervals [CIs] 1.29-8.69 and 1.06-8.10, respectively). Patients aged ≥ 65 years with stage IV breast cancer treated within 61-90 or ≥ 91 days after diagnosis had a 7.14- and 34.78-fold higher mortality risk (95% CIs 1.28-39.82 and 3.08-393.32, respectively). In conclusion, DFTI is associated with mortality in patients with stage II and IV breast cancer, especially at an older age.
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