by Naomi Noguchi, Michael Luke Marinovich, Elizabeth Jane
Wylie, Helen Gabriel Lund, Nehmat Houssami
The Breast: Published:January 27, 2022
Objectives
To determine screening outcomes in women who have no
recorded risk factors for breast cancer.
Methods
A retrospective population-based cohort study included all
1,026,137 mammography screening episodes in 323,082 women attending the
BreastScreen Western Australia (part of national biennial screening) program
between July 2007 and June 2017. Cancer detection rates (CDR) and interval
cancer rates (ICR) were calculated in screening episodes with no recorded risk
factors for breast cancer versus at least one risk factor stratified by age.
CDR was further stratified by timeliness of screening (<27 versus ≥27
months); ICR was stratified by breast density.
Results
Amongst 566,948 screens (55.3%) that had no recorded risk
factors, 2347 (40.9%) screen-detected cancers were observed. In screens with no
risk factors, CDR was 50 (95%CI 48–52) per 10,000 screens and ICR was 7.9
(95%CI 7.4–8.4) per 10,000 women-years, estimates that were lower than screens
with at least one risk factor (CDR 83 (95%CI 80–86) per 10,000 screens, ICR
12.2 (95%CI 11.5–13.0) per 10,000 women-years). Compared to timely screens with
risk factors, delayed screens with no risk factors had similar CDR across all
age groups and a higher proportion of node positive cancers (26.1% vs 20.7%).
ICR was lowest in screens that had no risk factors nor dense breasts in all age
groups.
Conclusions
Majority of screens had no recorded breast cancer risk
factors, hence a substantial proportion of screen-detected cancers occur in
these screening episodes. Our findings may not justify less frequent screening
in women with no risk factors.
