Ga-68 Pentixafor PET/CT in multiple myeloma and its correlation with clinical parameters – institutional pilot study

Objective: This study evaluates the role of Ga-68 Pentixafor PET/CT in staging and follow-up of multiple myeloma (MM) and its correlation with clinical parameters. Methods: Thirteen participants (9 males, 4 females; median age 65 years) with MM were recruited in this prospective observational study. Six participants were included for staging evaluation, seven were included for follow-up evaluation and underwent Ga-68 Pentixafor PET/CT. Focal PET-positive bone marrow lesions or diffuse bone marrow uptake (uptake more than liver) was considered a positive scan. Quantitative variables like SUVmax, SUVmean, total bone marrow volume and uptake (TBMV & TBMU) and tumor to background ratio (TBRmax) were obtained. Durie Salmon Plus Staging (DSPS) was used for MM staging by PET/CT and was compared with the International Staging System (ISS). Statistical comparison was performed between PET/CT quantitative variables and laboratory parameters. Results: Twelve participants (12/13) had positive Ga-68 Pentixafor PET/CT, among which one was diagnosed to have anaemia of chronic disease. One participant (1/13) who was clinically negative on follow-up had negative Ga-68 Pentixafor PET/CT. The sensitivity, specificity, PPV and NPV of Ga-68 Pentixafor PET/CT in MM (95% CI) was observed to be 100%, 50%, 91.6% and 100%, respectively. The correlation between DSPS and ISS in the patients who came for staging scans was found to be statistically significant (p-value 0.02). In quantitative analysis, either of the quantitative variables in Ga-68 Pentixafor PET/CT was positively correlated with clinical parameters related to tumor burden like CRAB score, Serum Protein Electrophoresis M-protein, beta 2 microglobulin, LDH, percentage of plasma cells infiltrates in bone marrow aspiration, ISS, serum free light chain and negatively correlated with haemoglobin, albumin (p-value < 0.5). Conclusion: Ga-68 Pentixafor PET/CT is a promising tracer and the only available non-invasive tool to assess the whole-body disease burden of CXCR4 receptors in staging and follow-up of MM. In addition, it has a vital role in the development of CXCR4-targeted theranostics. Dual tracer imaging using F-18 FDG and Ga-68 Pentixafor PET/CT may help in evaluating tumor heterogeneity in MM and add prognostic value at diagnosis and follow-up.