A Dramatic Response to Denosumab: Protracted Hypocalcemia Related to Human T-Cell Lymphotropic virus type 1-Associated Adult T-Cell Leukemia/Lymphoma

ABSTRACT Objective: Adult T-cell leukemia/lymphoma (ATL) is known for its aggressive behavior, frequently presenting with hypercalcemia. ATL tumor cells uniquely secrete parathyroid hormone-related protein, viral peptides, and inflammatory cytokines, inducing a state of high bone turnover and activation of the receptor activator of nuclear factor kappa-B signaling pathway resulting in hypercalcemia. Methods: A 54-year-old woman diagnosed with ATL presented with severe hypercalcemia refractory to bisphosphonate therapy. Treatment with denosumab was followed by protracted hypocalcemia and hypophosphatemia lasting approximately 5 months. Results: Hypercalcemia due to acute ATL was responsive in this case to denosumab therapy. Conclusion: Clinicians should be aware of the possibility of protracted hypocalcemia in patients with ATL exposed to denosumab therapy. Abbreviations: ATL = adult T-cell leukemia/lymphoma HTLV-1 = human T-cell lymphotropic virus type 1 IV = intravenous PTH = parathyroid hormone PTH-RP = parathyroid hormone-related protein RANK = receptor activator of nuclear factor kappa-B RANK-L = receptor activator of nuclear factor kappa-B ligand