^99mTc-MIBI whole body scintigraphy and P-glycoprotein for the prediction of multiple drug resistance in multiple myeloma patients

Multi-drug resistance (MDR) is a major challenge in the treatment of multiple myeloma (MM). There is low sensitivity of technetium-99m methoxy isobutyl isonitrile (^99mTc-MIBI) whole body scan (WBS) in the detection of active MM lesions, because 99Tc-MIBI is washed out from malignant cells in the presence of P-glycoprotein (PGP). The objective of the present cohort study was to evaluate of ^99mTc-MIBI WBS in the prediction of MDR in MM patients during a course of one year follow up. Thirty four patients with MM (25 male, 9 female of mean age 54.12±11.46 years) entered the study. Thirteen patients had no previous history of treatment and 21 had a history of previous chemo-radiotherapy. The diagnosis and staging of the disease were based upon routine laboratory and clinical criteria like bone marrow plasma cell count, serum M component, calcium, albumin, β₂- microglobulin. Measurements of PGP and WBS using ^99mTc-MIBI were performed before initialization of treatment and the response to treatment was assessed one year later. The baseline ^99mTc-MIBI WBS were considered positive for the detection of active lesions when at least one area of non-physiologic increased activity was noted. The follow up ^99mTc- MIBI WBS was positive for MDR when the patient had active disease but normal WBS. Our results showed that for WBS, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy in active state for the diagnosis of MDR were 38.9%, 62.5%, 70%, 31.2% and 46.1%, respectively. Also the above values for the detection of MDR, using PGP values were 50%, 50%, 69.2%, 30.8% and 50%, respectively. The relative risk of resistant to multiple regimens of chemotherapy after one year follow up in patients with negative to patients with positive ^99mTc-MIBI WBS was 1.02 (0.60-1.72). In conclusion, we found a low sensitivity of WBS and of PGP in the detection of MDR in patients with active MM. However, both WBS and PGP have 70% and 69% positive predictive value for MDR.