Benign breast disease and subsequent breast cancer: English record linkage studies.

BACKGROUND: Benign breast disease (BBD) increases the risk of breast cancer, but details of the relationship would benefit from further study in the UK.
METHODS: Analysis of linked statistical abstracts of hospital data, including a cohort of 20 976 women with BBD in an Oxford data set and 89 268 such women in an English national data set.
RESULTS: Rate ratios (RRs) for breast cancer, comparing BBD and comparison cohorts in these two data sets, were 2.3 (95% CI: 2.2-2.5) and 3.2 (3.0-3.3), respectively. RRs rose with increasing age at BBD diagnosis and remained elevated for at least 20 years after diagnosis. RRs were particularly high for a relatively small number of cancers occurring in the first few months after BBD diagnosis.
CONCLUSIONS: Our findings accord well with those in other large studies, mostly done in the USA, in showing a sustained long-term cancer risk after BBD. They also demonstrate that known long-term risks of disease can be reliably identified from linked routine administrative hospital statistics. Most other studies omit cancers in the first few months after BBD. Such cases-presumably either misdiagnosed or miscoded-merit further study to determine whether in fact they include diagnoses of cancer that were initially missed.