Abstract
OBJECTIVES: To evaluate the long term risks of invasive breast cancer and death related to breast cancer after non-screen detected ductal carcinoma in situ. Risks for women in the general population and for women diagnosed with ductal carcinoma in situ via the screening programme were compared. DESIGN: Population based cohort study. SETTING: Data from the National Disease Registration Service. PARTICIPANTS: All 27 543 women in England who were diagnosed with ductal carcinoma in situ, outside the NHS breast screening programme, during 1990 to 2018. MAIN OUTCOME MEASURES: Incident invasive breast cancer and death caused by breast cancer. RESULTS: By 31 December 2018, 3651 women with non-screen detected ductal carcinoma in situ had developed invasive breast cancer, more than four times higher than expected from national cancer incidence rates (ratio of observed to expected rate was 4.21 (95% conference interval 4.07 to 4.35)). The ratio of observed to expected rate of developing invasive breast cancer remained increased throughout follow-up among women aged <45-70 years. The 25 year cumulative risks of invasive breast cancer by age at diagnosis of ductal carcinoma in situ were 27.3% for <45 years, 25.2% for 45-49 years, 21.7% for 50-59 years, and 20.8% for 60-70 years. 908 women died of breast cancer, almost four times higher than that expected from breast cancer death rates in the general population (ratio of observed to expected rate 3.83 (3.59 to 4.09)). The ratio of observed to expected rate of mortality attributed to breast cancer remained increased throughout follow-up. The 25 year cumulative risks of breast cancer death by age at ductal carcinoma in situ diagnosis were 7.6% for <45 years, 5.8% for 45-49 years, 5.9% for 50-59 years, and 6.2% for 60-70 years. Among women aged 50-64 years, and therefore eligible for breast screening by the NHS, the ratio of observed to expected rate of invasive breast cancer in women with non-screen detected compared with screen detected ductal carcinoma in situ was 1.26 (95% conference interval 1.17 to 1.35), while the ratio for mortality from breast cancer was 1.37 (1.17 to 1.60). Among 22 753 women with unilateral ductal carcinoma in situ undergoing surgery, those who had mastectomy rather than breast conserving surgery had a lower 25 year cumulative rate of ipsilateral invasive breast cancer (mastectomy 8.2% (95% conference interval 7.0% to 9.4%), breast conserving surgery with radiotherapy 19.8% (16.2% to 23.4%), and breast conserving surgery with no radiotherapy recorded 20.6% (18.7% to 22.4%)). However, reductions did not translate into a lower 25 year cumulative rate of deaths attributable to breast cancer (mastectomy 6.5% (4.9% to 10.9%), breast conserving surgery with radiotherapy 8.6% (5.9% to 15.5%), breast conserving surgery with no radiotherapy recorded 7.8% (6.3% to 11.5%)). CONCLUSIONS: For at least 25 years after their diagnosis, women with non-screen detected ductal carcinoma in situ had higher long term risks of invasive breast cancer and breast cancer death than women in the general population. Additionally, they had higher long term risks than women with screen detected ductal carcinoma in situ. Mastectomy was associated with lower risks of invasive breast cancer than breast conserving surgery, even when accompanied by radiotherapy. However, risks of breast cancer death appeared similar for mastectomy, breast conserving surgery with radiotherapy, and breast conserving surgery with no radiotherapy recorded.