Recurrence of ductal carcinoma in situ: A large South American multicenter analysis.

e12612 Background: Although ductal carcinoma in situ (DCIS) has minimal mortality, recurrence rates after surgery are clinically relevant, and approximately half of recurrences are invasive, leading to a reduction in both overall and disease-specific survival. Numerous risk factors for recurrence have been identified; however, for certain features such as DCIS size and margin status, the association remains less clear. The objective was to analyze the association between clinical, pathological, and therapeutic characteristics and the risk of recurrence of primary pure DCIS. Methods: A retrospective evaluation was conducted in a large cohort of 1,270 patients from 24 centres from South American. Recurrence-free survival (RFS) was estimated using the Kaplan–Meier method, and comparisons between groups were performed using the Wilcoxon test. Univariate and multivariate Cox proportional hazards models were fitted to assess the association between the variables of interest and the risk of recurrence over time. A significance level of 0.05 was applied for all analyses. Results: Higher recurrence-free survival was observed in cases treated with breast-conserving surgery, radiotherapy, adjuvant endocrine therapy, smaller tumor size, and nuclear grade 1 or 2. No significant differences in recurrence-free survival were found according to margin status. For each 5-mm increase in tumor size, the risk of recurrence increased by 6% (HR 1.06; 95% CI 1.01–1.13; p = 0.0378). Participants who did not receive endocrine therapy had a 119% higher risk of recurrence compared with those who did (HR 2.19; 95% CI 1.24–3.86; p = 0.006). Low-grade DCIS (nuclear grade 1 and 2) showed a 53% lower risk of recurrence than high-grade DCIS (HR 0.47; 95% CI 0.28–0.78; p = 0.0033). After adjustment in the multivariate model, only nuclear grade remained a significant independent predictor, with low-grade DCIS exhibiting a 45% lower risk of recurrence compared with grade 3 disease (HR 0.55; 95% CI 0.32–0.94; p = 0.03). Conclusions: These findings confirm the inherent complexity of identifying factors associated with recurrence risk in DCIS. While tumor size, absence of endocrine therapy, and high nuclear grade were significantly associated with higher risk of recurrence in the univariate analyses, only nuclear grade retained an independent and significant association in the multivariate analysis. This underscores the central prognostic role of nuclear grade and highlights the limitations of interpreting other clinical and therapeutic factors in isolation. Given the overall low recurrence rate of DCIS, larger studies with long-term follow-up are needed to refine risk stratification, optimize therapeutic decision-making, and advance toward more personalized management strategies, avoiding both undertreatment and overtreatment.