This summary table contains detailed information about research studies. Summary tables offer an informative look at the science behind many breast cancer guidelines and recommendations. However, they should be viewed with some caution. In order to read and interpret research tables successfully, it is important to understand some key concepts. Learn how to read a research table.
Introduction: Hyperplasia is a benign breast condition where some breast cells are dividing more quickly than normal. There are two types of hyperplasia: atypical and usual.
In atypical hyperplasia, the dividing cells look abnormal under a microscope. With usual hyperplasia, the dividing cells look normal.
Findings from the cohort and nested case-control studies below show both types of hyperplasia increase the risk of breast cancer, but atypical hyperplasia increases risk to a greater degree than usual hyperplasia does.
Learn more about hyperplasia and breast cancer risk.
Learn more about benign breast conditions.
Learn about the strengths and weaknesses of different types of studies.
See how this risk factor compares with other risk factors for breast cancer.
Study selection criteria: Prospective cohort and nested case-control studies with at least 60 cases and meta-analyses.
Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Study Population(number of participants)
Relative Risk of Breast Cancer in Women with HyperplasiaCompared to Women without Hyperplasia,by Type,RR (95% CI)
Prospective cohort studies
Breast Cancer Surveillance Consortium 
42,818 (1,359 cases)
Hartmann et al. 
Breast Cancer Prevention Trial-NSABP 
Nested case-control studies
Dupont et al. 
Kabat et al. 
Nurses' Health Study and Nurses' Health Study II 
Breast Cancer Detection Demonstration Project 
Palli et al. 
Relative Risk of Breast Cancer in Women with Hyperplasia Compared to Women without Hyperplasia, by Type,RR (95% CI)
Dyrstad et al. 
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