Cancer outcomes in women without upfront surgery for ductal carcinoma in situ: observational cohort study

Abstract Objective To determine the risk of subsequent ipsilateral invasive breast cancer in women who do not receive upfront surgery on diagnosis of ductal carcinoma in situ (DCIS). Design Observational cohort study using data abstracted directly from patients’ medical records and from a national cancer registry in patients with primary DCIS diagnosed between 2008 and 2015. Setting Commission on Cancer accredited facilities (n=1330) in the US. Participants 1780 women with diagnosis of primary DCIS on needle biopsy who were alive and free of invasive breast cancer at 6 months after diagnosis. Interventions No surgery within 6 months of diagnosis. Main outcome measures Primary outcome: ipsilateral invasive breast cancer; secondary outcome: death due to breast cancer. Subgroup analysis by risk status, based on eligibility criteria of ongoing active monitoring trials: low risk if aged ≥40 years at diagnosis of an imaging detected, nuclear grade I/II, and hormone receptor positive DCIS; high risk otherwise. Results Median age at diagnosis was 63 years, and median follow-up was 53.3 months. Among all 1780 women, the number of ipsilateral invasive breast cancer events was 115 (6.5%) and the number of deaths from breast cancer was 29 (1.6%). The 8 year cumulative incidence of ipsilateral invasive breast cancer was 10.7% (95% confidence interval (CI) 8.4% to 12.8%). Incidence of invasive cancer differed by both disease and patient related factors, with 8 year cumulative incidences of ipsilateral invasive breast cancer ranging from 8.5% (95% CI 4.7% to 12.1%) among women at low risk (n=650) to 13.9% (10.5% to 17.2%) among those at high risk (n=833). The 8 year disease specific survival probability was 96.4% (95% CI 95.0% to 97.9%) overall and 98.1% (96.7% to 99.6%) among women at low risk. Conclusions In a cohort of patients who did not receive initial surgery for DCIS, the 8 year cumulative incidence of invasive cancer in the same breast varied between 8% and 14%. Effective risk stratification tools and shared decision making are essential for this patient population.