Peripheral Blood Monocyte Count is a Dynamic Prognostic Biomarker in Multiple Myeloma.

With growing knowledge of multiple myeloma (MM) pathobiology and the introduction of novel therapies, risk stratification continues to evolve. Myeloid-derived suppressor cells and tumor-associated macrophages, derived from peripheral blood monocytes, support malignant plasma cell proliferation in the bone marrow. Since peripheral blood absolute monocyte count (AMC) is thought to could reflect the bone marrow microenvironment, we sought to evaluate the prognostic significance of AMC in MM. We retrospectively analyzed 10,822 patients with newly-diagnosed MM between 2000 and 2019 at Veteran's Administration hospitals. We obtained AMC closest to diagnosis and every 3 months thereafter up to 2.5 years. Patients were stratified into 4 groups: low, normal, elevated, and severely elevated AMC (AMC 0.2, 0.2 to < 0.8, 0.8-1.25 and > 1.25 x103/mm3, respectively). Abnormal AMC at diagnosis was observed in 25.3% of patients and was associated with inferior overall survival (OS). In patients with low, elevated, severely elevated, and normal AMC, At diagnorespectively, sis, median OS at diagnosis was 2.3, 2.7, 3.1, 3.6 years (p < 0.001), and at 2.5 years median OS at 2.5 years was 2.0, 2.6, 3.4, 3.9 years (p < 0.001) in patients with low, elevated, severely elevated, and normal AMC, respectively. Patients with normal AMC at diagnosis who developed an abnormal AMC > 1 year after diagnosis also had inferior OS relative to patients who maintained a normal AMC. Abnormal AMC was also associated with inferior OS independent of validated prognostic markers including the international staging system stage ISS Stage, and high lactate dehydrogenase LDH. Our findings provide novel clues for future prospective studies on the functional role of monocytes in multiple myeloma, which could be a readily available metric for risk stratification.