Abstract 199P
Background
Cancer overdiagnosis is the detection by screening of asymptomatic subjects of a cancer that would not be life-threatening during subject lifetime. Most studies that have evaluated overdiagnosis of screening mammography in general populations were based on time trend projections or on statistical models using unverified assumptions. Since 1988, the NHS Breast Screening Programme (NHSBCSP) in England invites every three years women aged 50 to 65 (1988-2001), and 50 to 70 (2002-2019) years to screening mammography. This study estimates the excess in situ and invasive breast cancers (II-BC) in the NHSBCSP using a new approach based on real-world data on screening mammography activities in England.
Methods
Data from two publicly available sources were used: the breast cancer incidence data in England from the Office of National Statistics and the annual reports on the NHSBCSP from 1995 to 2019. The first source provided numbers of II-BC diagnosed each year in 5-year age groups of women. The second source provided (1) the number of resident women eligible for screening who had at least one screen the last three years, (2) the numbers of women invited to screening, and (3) the numbers of II-BC found at screening by 5-year age group. For each year, interval II-BC were estimated using interval II-BC rates reported in the literature on the NHSBCSP. Using these data, excess number of II-BC among women participating to screening were estimated.
Results
Incidence rates of screen-detected and of interval breast II-BC per 100,000 women participating to screening ranged from 313 in 1995 to 403 in 2019. Incidence rates among women not participating to screening ranged from 240 in 1995 to 314 in 2019. From 1995 to 2019, compared to women not participating to screening, there was a median 24% (IQR: 20%-28%) excess II-BC among women participating to screening. These excess II-BC represented 33% of all screen-detected cancers.
Conclusions
A novel approach based on real-world data showed that the NHSBCSP is associated with an excess number of II-BC that amounts to one quarter of all II-BC cancers found among participating women. Probably that most of this II-BC excess would not be diagnosed in the absence of screening.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Philippe Autier.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.