Breast Cancer risk in patients with dopamine agonist-treated hyperprolactinemia.

Purpose: 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.

Methods: 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.

Results: 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).

Conclusion: 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.