Recent cohort studies demonstrated better overall survival (OS) or breast cancer-specific survival (BCS) for breast-conserving therapy (BCT) followed by radiation (RT) compared to mastectomy alone (MT). This is the first observational study in which adjustments for a comprehensive set of prognostic factors, adjuvant therapies, mode of detection, and comorbidities were possible to investigate OS, BCS, as well as recurrence risk of patients undergoing BCT + RT, MT + RT, or MT.

Women aged 50-74 years at diagnosis of early-stage invasive breast cancer (I-IIIa) between 2001 and 2005 at the German population-based case-control study (MARIE study) were recruited and followed prospectively as a case cohort until 2015. Kaplan-Meier estimates and stepwise adjusted multivariable Cox models were used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CI).

The 2762 patients included were followed up for a median of 11.9 years (95% CI 11.8-12.0). 74.2% of patients underwent BCT + RT; 10.3% MT + RT and 15.6% MT alone. Compared to patients treated with MT alone, patients treated with BCT + RT showed non-statistically significant improved OS (HR 0.79, 95% CI 0.61-1.02), BCS (HR 0.79, 95% CI 0.55-1.12), and no difference in recurrence risks (HR 1.01, 95% CI 0.74-1.37). For patients treated with MT + RT, there were no differences in OS (HR 1.06, 95% CI 0.75-1.50), BCS (HR 1.17, 95% CI 0.75-1.82), or recurrence risk (HR 1.33, 95% CI 0.89-1.97).

Among patients with early-stage breast cancer, clinical outcomes more than 10 years after diagnosis did not differ between the primary treatment options BCT + RT, MT + RT versus MT alone after full adjustment.