Endocrine Abstracts

Introduction: Parathyroid carcinoma (PC) is one of the rarest malignant endocrine neoplasms (0.005% of all oncological diseases). PC relapses in 40-60% cases. The severity of the disease is determined by life-threatening hypercalcemia. Surgery is the gold treatment standard of primary tumors and distant metastases, but if it is contraindicated there are few options to control life-threatening hypercalcemia.

Case 1: A 36-year-old-woman with a recurrent parathyroid carcinoma (PC) after multiple surgeries was admitted with symptoms of hypercalcemic crisis. Laboratory test revealed severe hypercalcemia - 4.62 mmol/l (2.15-2.55), elevated PTH - 265 pmol/l (2.0-9.4), hypophosphatemia - 0.58 mmol/l (0.74-1.52) while taking zoledronic acid 4 mg/month for 11 months and cinacalcet 90 mg/day (further dose titration lead to dyspepsia). The PET-CT with 18-FDG showed metastases in both lungs, pleura, multiple bones and liver. Due to ineffectiveness of previous therapy, we initiated denosumab 120 mg/28 days with a significant clinical and laboratory improvement. 3 months later Ca adj. was 2.6 mmol/l without cinacalcet therapy.

Case 2: A 70-year-old woman with a PC relapse and distant lung metastases complaining of muscle weakness, adynamia, bone pain and hoarseness was hospitalized in our Centre. Laboratory examination showed hypercalcemia - 4, 04 mmol/l, increased PTH - 1148 pg/ml and low eGFR (CKD-EPI) - 32 ml\min\1.73 m². We initiated infusion therapy, cinacalcet and denosumab 60 mg with the achievement of normocalcemia - Ca adj. 2.26 mmol/l on the 14th day. She was discharged under cinacalcet 60 mg/day. 6 months later she was admitted again with symptomatic hypercalcemia - Ca adj. 4, 13 mmol/l and reduced eGFR (CKD-EPI) - 27 ml/min/1.73 m². We started infusion therapy, titrated cinacalcet to 90 mg/day and provided injection of denosumab 60 mg. 7 days after Ca adj. was 2.9 mmol/l, eGFR (CKD-EPI) - 42 ml/min/1.73 m². Failure to achieve significant calcemia reduction we prescribed denosumab 120 mg/28 days with cinacalcet titration to 120 mg/day under regular laboratory follow-up

Conclusion: Managing a recurrent PC is challenging. Denosumab is a therapy of choice in bisphosphonate/calcimimetics refractory hypercalcemia and low eGFR.