Previous studies have found an association between elevated circulating
prolactin levels and increased risk of
breast cancer.
Prolactin stimulates
breast cancer cell proliferation, migration, and survival via binding to the cell-surface
prolactin receptor. The association of
prolactin receptor expression with breast
tumorigenesis remains unclear as studies that have focused on this association have had limited sample size and/or information about
tumor characteristics. Here, we examined the association of
prolactin expression with
tumor characteristics among 736 cases, from a large population-based case-control study of
breast cancer conducted in Poland (2000-2003), with detailed risk factor and pathology data.
Tumors were centrally reviewed and prepared as tissue microarrays for immunohistochemical analysis of
prolactin receptor expression. Association of
prolactin receptor expression across strata of
tumor characteristics was evaluated using χ (2) analysis and logistic regression.
Prolactin receptor expression did not vary by menopausal status; therefore, data from pre- and post-menopausal women were combined in the analyses. Approximately 83 % of breast
cancers were categorized as strong
prolactin receptor staining. Negative/low
prolactin receptor expression was independently associated with poorly differentiated (p = 1.2 × 10(-08)) and larger
tumors (p = 0.0005). These associations were independent of
estrogen receptor expression. This is the largest study to date in which the association of
prolactin receptor expression with
tumor characteristics has been evaluated. These data provide new avenues from which to explore the associations of the
prolactin/
prolactin receptor signaling network with breast
tumorigenesis.