Concomitant Primary Hyperparathyroidism in Patients with Multiple Myeloma: A Possible Link?

Hypercalcemia is a significant feature of patients with active multiple myeloma (MM) with extensive bone disease. Among the causes of non-neoplastic hypercalcemia, primary hyperparathyroidism (PHPT) is one of the most common, leading to osteoporosis and bone fractures. Interestingly, some preclinical data indicate that high secretion of parathyroid hormone (PTH) may have a negative impact on bone disease and MM progression. However, concomitant diagnosis of MM and PHPT has rarely been described. Here, we present 4 cases of patients with active MM and hypercalcemia with high or inappropriately normal PTH levels. Interestingly, CD138+ cells from these 4 MM patients lack PTH receptor 1 and PTH-related peptide expressions, indicating that PTH could have a paracrine rather than a direct pro-tumoral effect. Moreover, these cases suggest that the concomitant diagnosis of MM and PHTP may not be so rare and should be considered for the clinical management of MM patients with hypercalcemia.