18F-FDG PET/CT AND 99MTC-MIBI SCINTIGRAPHY LOCALIZE ACTIVE MYELOMA LESIONS AND CORRELATE WITH INCREASED SERUM LEVELS OF THYMIDINE KINASE DETECTED BY NOVEL METHOD DIVITUM™

ABSSUB-3941

Background: Cell proliferation activity is a central independent prognostic factor and one of the targets for personalized

and risk-adapted treatment in multiple myeloma (MM). Increased activity of thymidine kinase (TK) in
serum is associated with higher proliferation rates in hematological malignancies. Imaging methods such as 99mTc-MIBI scintigraphy or 18F-FDG PET/CT can visualize active myeloma lesions and their positivity is a negative prognostic factor.

Aims: The study aimed at comparing two methods for evaluating thymidinekinase TK in serum – an older RIA method and novel DiviTum™ – in patients with MM and MGUS, and also comparing them with biochemical markers and degree of activity evaluated by imaging methods 99mTc-MIBI scintigraphy and 18F-FDG PET/CT.

Methods: Serum thymidinekinase TK levels were evaluated by DiviTum™ and an RIA method (TK REA kit by Immunotech);The study analyzed correlation of TK activity in serum with biochemical markers reflecting activity of MM: β2-m, LDH, the ratio of kappa to lambda (κ/λ) free light chains and percentage of bone marrow plasma cells (BMPC). 99mTc-MIBI scintigraphy and 18F-FDG PET/CT were performed at the time of diagnosis. The degree of activity was expressed semiquantitatively. Scans were classified as 0 (normal activity), 1 (diffuse positivity) or 2 (focal positivity).

Results: We found a strong positive correlation between TK in serum evaluated by DiviTum™ and by TK REA.. The DiviTum™ analytic method extended the detection range and was able to detect higher levels of TK than the RIA method. DiviTum™ technique found positive correlation with β2-m (r = 0.497) and LDH (r = 0.502) and moderate positive correlation with BMPC (r = 0.368). Significantly higher TK values measured by TK REA and DiviTum™ in the group of patients with MM (stages I, II or III) than in those with MGUS. Increased TK levels were observed in MIBI- or PET/CT-positive patients. Analysis of repeated measurements of TK in serum during treatment of MM patients found a correlation between change in TK measured by DiviTum™ and LDH during treatment.

Summary/Conclusion: Analysis revealed a significant correlation between TK in serum and LDH, β2-m and BMPC. Increased levels of TK in serum were observed in MIBI- or PET/CT-positive patients. Combination of positivity of imaging methods which can localize active tumor lesions and increased levels of TK in serum can have an impact on decision-making and optimization of the therapeutic approach.

This work was supported by grant IGA MZ ČR NT 12215-4/2011, IGA MZ ČR NT 14393 and by the research project Biomedreg CZ.1.05/2.1.00/01.0030.

Keywords: MGUS, Multiple myeloma, PET

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