High density of tryptase-positive mast cells in patients with multiple myeloma: correlation with parameters of disease activity.

Multiple myeloma (MM) is a plasma cell neoplasm characterized by bone marrow infiltration from malignant plasma cells. Mast cells play an important role in inflammation and angiogenesis in malignant diseases. The aim of the study was to evaluate the mast cell density in bone marrow of untreated MM patients with markers of disease activity such as serum interleukin-6 (IL-6), B2M, and C-reactive protein (CRP), the grade of bone marrow infiltration, and the levels of produced paraprotein. We studied 86 newly diagnosed MM patients (46 males, 40 females, mean age 59 ± 13.7 years). Thirty of them reached plateau phase after chemotherapy and 20 healthy volunteers. According to the criteria of International Staging System (ISS) staging system, 23 patients had stage I, 30 had stage II, and 33 had stage III. The serum concentrations of CRP, B2M, and IL-6, and the mast cell density (MCD) values were significantly higher in MM patients' group (1.6 ± 1.8, 4.3 ± 2.9, 7.1 ± 5.1, and 9 ± 4.8), in comparison with those found in control group (0.4 ± 0.1, 1.5 ± 0.6, 1.1 ± 0.5, and 1.9 ± 0.7; p < 0.001 in all the cases). Significant differences were found between the grade of infiltration in bone marrow, and the paraprotein values in patients' serum before and after chemotherapy. Furthermore, there was a significant correlation between the MCD values and the prognostic markers CRP (r = 0.452, p < 0.0001), IL-6 (r = 0.475, p < 0.0001), bone marrow infiltration (r = 0.333, p < 0.0002), and serum paraprotein levels(r = 0.221, p < 0.04). High MCD values strengthen the hypothesis that mast cells participate in the pathogenesis of disease progression and may be used as an indicator of the disease activity.