Serum Level Of Parathyroid Hormone Is Associated With Risk Factors and Clinical Outcomes In Multiple Myeloma

Parathyroid hormone (PTH) is synthesized and secreted by the chief cells of the parathyroid gland. PTH has a positive impact on hematopoietic stem cells by indirectly decreasing hematopoietic cell apoptosis, and is currently being investigated as a potential therapeutic to stimulate hematopoiesis and enhance bone marrow engraftment. According to previous study, it was hypothesized that elevated PTH may mediate the induction of multiple myeloma (MM) through the biologic effects of IL-6. However, there was no comprehensive study regarding clinicopathological implications of PTH in MM. This study investigated the pathological and clinical implications of serum PTH in MM patients and relationship with other risk factors of MM.

A total of 115 patients who were newly diagnosed with MM were enrolled between 2006 and 2012. Serum PTH level was measured by automated 2-site chemiluminescent sandwich assay (Abbott Diagnostics). The medical parameters were reviewed for age, sex, PTH, plasma cell percentage in bone marrow, serum M protein, immunoglobulin level, free light chain (FLC) - kappa and lambda, FLC ratio, calcium, creatinine, hemoglobin, albumin, beta-2 microglobulin, lactate dehydrogenase (LDH), international staging system (ISS) stage, international myeloma working group (IMWG) response, chromosome abnormality, bone lesion, treatment outcome, and so on. The collected data was analyzed by PASW 18.0. We performed Spearman’s correlation analysis, Mann Whitney U-test, Kruskall Wallis test, time dependent Cox regression analysis, survival analysis by Kaplan-Meier method, etc.

Serum PTH level of 115 myeloma patients was 24.7±34.9 (ranged 0.0-284.1) pg/mL. Serum level of IgG, IgM, FLC-lambda, albumin, and LDH was in positive correlation with serum PTH. Age, plasma cell percentage, M protein, IgA, FLC-kappa, FLC ratio, calcium, creatinine, hemoglobin, and beta-2 microglobulin showed negative correlation with PTH. Among those above, IgM (rho=0.190, p=0.045) and calcium (rho=-0.220, p=0.043) revealed statistically significant correlation with serum PTH. Serum PTH level in MM patients was not significantly different according to the group of IMWG response (p=0.450) and ISS stage (p=0.414). Meanwhile, there was no significant difference of PTH according to chromosomal abnormality (p=0.353), bone lesion (p=0.207), and disease progression (p=0.322). Besides, only calcium level was meaningfully different (p=0.016) by the comparison of clinical parameters between MM patient’s group with high PTH level and non-high PTH group (cut-off PTH level=68.3 pg/mL, Mann Whitney U-test). Relative to non-high PTH (<68.3 pg/mL) group, the hazard ratio was higher for group with high PTH level (≥68.3 pg/ml) ([HR] 3.037; p=0.524; 95% CI, 0.100∼92.586; Table 1). With regard to the prognostic implication of serum PTH value, the patient group with above 68.3 pg/mL showed moderate, inferior progression free survival (PFS) than non-high PTH group (median, 5 months vs. 13 months, p=0.056, Fig.1B). However, no overall survival (OS) differences were found between high PTH group and non-high PTH group (Fig. 1A). Interestingly, subgroup analysis showed that patients with high PTH level significantly had an inferior PFS than those with non-high PTH level. In detail, the subgroup were as follows; patients who reached the complete remission (CR) state (N=25) defined by IMWG response criteria at the end of follow up period (median, 3 months vs. 41 months, p=0.001, Fig.1C), patients (N=41) who belonged to ISS stage II (median, 1 months vs. 15 months, p=0.006, Fig.1D), patients (N=97) with no chromosome abnormality (median, 4 months vs. 15 months, p=0.034, Fig.1E), patients (N=28) who have undergone transplantation (median, 3 months vs. 18 months, p=0.009, Fig.1F).

This study showed that blood PTH level in MM at diagnosis was associated with risk factors and clinical outcome in MM patients.

No relevant conflicts of interest to declare.