PRIMARY HYPERPARATHYROIDISM AND SERUM CALCIUM IN BREAST CANCER PATIENTS EVALUATED FOR LOW BONE MASS - A SINGLE CENTER EXPERIENCE.

The bone health guidelines for breast cancer (BC) patients recommend bone mineral density (BMD) testing. Patients with low BMD and elevated serum calcium levels (SCLs) are further evaluated for primary hyperparathyroidism (PHPT). We aimed to determine the prevalence of PHPT in treated BC patients with low BMD and analyze the association of SCLs with histopathologic tumor features and cancer treatment. This retrospective study included postmenopausal BC patients examined at Osteoporosis Clinic between 2013 and 2020. Clinical and BMD data were collected from patient medical records. Patients with biochemical suspicion of PHPT underwent standard parathyroid imaging procedures. Nine out of 137 (6.6%) patients were diagnosed with PHPT; 8/9 patients underwent parathyroidectomy and one patient was advised to follow-up. Among the rest of 128 non-PHPT patients, higher SCLs showed a trend of positive association with higher tumor grade and axillary lymph node involvement, and received immunotherapy, although without statistical significance. We found a higher prevalence of PHPT in treated BC patients compared to the general population. Higher SCLs show a trend of positive correlation with some more aggressive histopathologic tumor features and with immunotherapy. The results of this study suggest that assessment of SCLs should be routinely performed to rule out PHPT in treated BC patients with low BMD.