The Women's Health Initiative Observational Study on postmenopausal women also suggests that the association between breast cancer risk and carotenoids differs by estrogen receptor (ER) and progesterone receptor (PR) status since this study found that dietary alpha-carotene and beta-carotene were inversely associated with the risk of ER+PR+ breast cancer only, but not with other breast cancer groups defined by ER and PR status [32]. Here, PGR is linked to breast cancer.