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.