Treatment and Outcome of Ductal Carcinoma in Situ for the German Federal States Berlin and Brandenburg in the Period 2007-2020.

Ductal carcinoma in situ (DCIS) of the female breast is treated with surgery possibly followed by radiotherapy (RT) and/or adjuvant hormonal therapy despite their known long-term side effects. Since not every DCIS will progress into an invasive breast cancer (IBC), disease progression and de-escalation of treatment is an important topic of current research. During 2007-2020, 3905 individuals with a DCIS diagnosis were reported to the cancer registry of Brandenburg and Berlin. We selected 3424 women who were cancer-free prior to DCIS diagnosis and without synchronous diagnoses of DCIS or ipsilateral IBC (iIBC). The objective was to describe changes over time in DCIS treatment and risk of developing iIBC by treatment. We observed decreasing proportions of mastectomy, breast-conserving surgery (BCS) with RT, and standard versus hypofractionated RT over time. During a median follow-up of 3.8 years, 105 women developed iIBC. Compared with BCS + RT with standard fractionation (54.9%, 1878/3424, 53 iIBC events), hazard ratios (HR) for ilBC were 0.72 (95% confidence interval [CI] 0.26, 1.99; 4 events) for BCS + hypofractionated RT, 0.70 (95% CI 0.33, 1.41; 11 events) for BCS alone, and 0.83 (95% CI 0.50, 1.37; 26 events) for mastectomy. Analyses were adjusted for DCIS size, grade, residual tumor status and ECOG score. We observed a de-escalation of treatment over time, with fewer mastectomies, less RT, and more hypofractionation of RT. No substantial differences in risk of iIBC were observed between these treatments. There is a need to evaluate DCIS treatment de-escalation in larger cohorts with longer follow-up.