Breast Cancer risk in patients with dopamine agonist-treated hyperprolactinemia

Given prolactin's (PRL) multifaceted roles in mammary tissue, an association between hyperprolactinemia and breast cancer has been hypothesized. Despite previous studies not identifying this risk, we aimed to investigate whether a connection exists.

This retrospective cohort study compared breast cancer incidence in patients with dopamine agonist (DA)-treated hyperprolactinemia versus matched controls in a 1:5 ratio. The primary outcome was a breast cancer diagnosis following hyperprolactinemia diagnosis.

The cohort consisted of 1484 female patients with DA-treated hyperprolactinemia matched to 7418 female controls (mean age at diagnosis 32.70 ± 11.12 years; BMI 25.60 ± 5.84 kg/m²). Breast cancer was diagnosed in 27 patients with hyperprolactinemia (1.82%) and 97 controls (1.31%) (HR 1.40, 95% CI 0.91-2.14, p = 0.12). Patients who developed breast cancer were diagnosed with hyperprolactinemia later in life than those who did not (median age 42.63 vs. 29.79 years; p < 0.0001). Patients with PRL < 5× upper limit of normal (ULN) at diagnosis developed breast cancer at a higher rate than controls (2.25% vs. 1.33%; HR 1.73, 95% CI 1.09-2.75), but the difference was not significant in patients with PRL ≥ 5×ULN. Patients who exhibited longer times to PRL normalization had higher incidence of breast cancer (median 2.60 vs. 1.41 years in those who did not develop breast cancer; p = 0.03).

Overall, patients with DA-treated hyperprolactinemia did not show an increased risk for breast cancer compared to controls. However, the risk was significantly higher among those whose PRL levels were < 5×ULN, had advanced age of diagnosis, or prolonged time to PRL normalization.