This summary table contains detailed information about research studies. Summary tables are a useful way to look at the science behind many breast cancer guidelines and recommendations. However, to get the most out of the tables, it’s important to understand some key concepts. Learn how to read a research table.

Introduction: Prolactin is a natural hormone in the body. It plays a role in breast growth and the production of milk during breastfeeding.

Women with higher blood levels of prolactin have a slightly higher risk of breast cancer than women with lower levels.

Learn more about prolactin and breast cancer risk.

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 nested case-control studies with at least 100 breast cancer cases and meta-analyses.

Table note: Relative risks above 1 indicate increased risk. Relative risks below 1 indicate decreased risk.   

Study	Study Population (number of participants)		Risk of Breast Cancer in Women with Higher Blood Prolactin Levels Compared to Women with Lower Levels Relative Risk (95%CI)
			Before Menopause	After Menopause
Nested case-control studies
	Cases	Controls
EPIC cohort [1]	2,250	2,250	0.70 (0.48-1.03)	1.29 (1.05-1.58)
Nurses’ Health Study and Nurses’ Health Study II [2]	1,539	2,681	1.4 (1.0-1.9)	1.3 (1.1-1.7)
KARMA study [3]	721	1,400	1.77 (1.00-3.12)	1.03 (0.70-1.51)
Malmo Diet and Cancer Study and Northern Sweden Health and Disease Study [4]	173	438		1.34 (0.83-2.17)
Wang et al. [5]	111	3,665	1.07 (0.51-2.23)	1.63 (0.57-4.71)
Meta-analyses
Wang et al. [6]	7 studies		0.99 (0.84-1.16)	1.27 (1.13-1.43)

References

1. Tikk K, Sookthai D, Johnson T, et al. Circulating prolactin and breast cancer risk among pre- and postmenopausal women in the EPIC cohort. Ann Oncol. 2014 Jul;25(7):1422-8, 2014.
2. Tworoger SS, Eliassen AH, Sluss P, Hankinson SE. A prospective study of plasma prolactin concentrations and risk of premenopausal and postmenopausal breast cancer. J Clin Oncol. 25(12):1482-8, 2007.
3. Gabrielson M, Ubhayasekera K, Ek B, et al. Inclusion of plasma prolactin levels in current risk prediction models of premenopausal and postmenopausal breast cancer. JNCI Cancer Spectr. 2(4):pky055, 2018.
4. Manjer J, Johansson R, Berglund G, et al. Postmenopausal breast cancer risk in relation to sex steroid hormones, prolactin and SHBG (Sweden). Cancer Causes Control. 14(7):599-607, 2003.
5. Wang DY, De Stavola BL, Bulbrook RD, et al. Relationship of blood prolactin levels and the risk of subsequent breast cancer. Int J Epidemiol. 21(2):214-21, 1992.
6. Wang M, Wu X, Chai F, Zhang Y, Jiang J. Plasma prolactin and breast cancer risk: a meta- analysis. Sci Rep. 6:25998, 2016.