MON-772 Prevalence of Primary Hyperparathyroidism in Patients With Breast Cancer - A Retrospective, Single Institution Study

Abstract Disclosure: P. Pile: None. J. Arunachalam: None. P. Madhavan: None. Background: Previous studies have suggested an increased risk of malignancy in patients with primary hyperparathyroidism (PHPT), with one notable association being breast cancer, as highlighted in a 2007 Swedish study by Nilsson et al. Breast cancer is frequently linked to hypercalcemia of malignancy, which is often a sign of skeletal metastases. However, there is limited information on hypercalcemia in patients with breast cancer unrelated to skeletal metastases. Here, we present a retrospective, single institution study evaluating the prevalence of primary hyperparathyroidism in breast cancer. Methods: After receiving exemption from the institutional review board, we conducted a review of electronic medical records from our institution to assess the prevalence of hyperparathyroidism in breast cancer patients between July 2018 to December 2024. We used diagnosis codes for breast cancer and hyperparathyroidism to identify relevant patients. The study population consisted of all patients diagnosed with hyperparathyroidism (HPT), excluding those with chronic kidney disease (CKD), as these individuals might have secondary or tertiary hyperparathyroidism. Specifically, patients with CKD stages 3a, 3b, 4, and 5 were excluded from the analysis. Data collection was performed using Slicer Dicer in Epic, and descriptive statistics were applied to determine the proportion of patients with Vitamin D deficiency and bone metastases in patients with HPT and breast cancer, and prevalence of HPT. To compare prevalence rates, a Chi-square test was used. Results: The study identified 72 female breast cancer patients, aged 73 ± 10 years, who were diagnosed with HPT but did not have CKD. The prevalence of HPT in this group was found to be 2.12% (n=72), which is significantly higher than the prevalence of HPT in general population of 0.11% (n=1862), with a p-value < 0.001. Only 5 patients (0.07%) had distant bone metastases. Only 3 (0.04%) patients had Vitamin D deficiency (25-OH-D <20 ng/mL) at the time of elevated parathyroid hormone (PTH) levels, further supporting that elevated PTH was likely due to PHPT rather than secondary causes. Conclusion: This study reveals a significantly higher prevalence of PHPT in the breast cancer population compared to the general population. This study underscores the importance of evaluating PTH in patients with breast cancer and hypercalcemia even without the presence of bone metastases. Limitations of our study include the inclusion of males in the general population cohort, who have a lower prevalence of breast cancer. To address these limitations, we plan to further analyze patient characteristics in a future study to refine our findings and reduce such confounders. Presentation: Monday, July 14, 2025