AIM: Technetium-99m 2-methoxy-isobutyl-isonitrile ([99mTc] MIBI) has been successfully used to study patients with multiple myeloma (MM). This tracer is also a substrate for P-glycoprotein (Pgp). Since Pgp overexpression is one of the primary mechanisms of multidrug resistance in MM, the aim of this study was to test whether [99mTc] MIBI could be an index of Pgp overexpression and function in MM and therefore predicts response to chemotherapy. METHODS: Forty patients with MM (12 in stage I, 15 in stage II, and 13 in stage III) showing diffuse bone marrow [99mTc] MIBI uptake were included in the study. All patients underwent whole body scintigraphy at 10 and 60 minutes after i.v. injection of 555 MBq of [99mTc] MIBI. [99mTc] MIBI washout was measured, after decay correction, as: (10 minute counts/pixel minus 60 minute counts/pixel) divided by 10 minute counts/pixel, computed on a region of interest drawn on the thoracic spine (posterior projection), taking care of avoiding heart and splanchnic organs. Disease restaging was performed at a mean time of 32+/-20 months, and patients were considered to be in remission (complete or partial) or to show disease progression on the basis of a complete clinical and hematological evaluation. RESULTS: Patients showing disease progression at restaging (n=26) had higher washout (19.3+/-9.8% vs 12.8+/-6.9%, p<0.05) than patients in remission (n=14). Disease free survival was significantly better in patients with lower washout of [99mTc] MIBI. No differences in therapeutic regimen and stage of disease at admission were found between the 2 groups. When patients treated with melphalan were excluded from the analysis, 87.5% of patients in remission had low washout. CONCLUSIONS: The present study suggests a potential role of [99mTc] MIBI washout in predicting response to chemotherapy in patients with MM.
AIM: Technetium-99m 2-methoxy-isobutyl-isonitrile ([99mTc] MIBI) has been successfully used to study patients with multiple myeloma (MM). This tracer is also a substrate for P-glycoprotein (Pgp). Since Pgp overexpression is one of the primary mechanisms of multidrug resistance in MM, the aim of this study was to test whether [99mTc] MIBI could be an index of Pgp overexpression and function in MM and therefore predicts response to chemotherapy. METHODS: Forty patients with MM (12 in stage I, 15 in stage II, and 13 in stage III) showing diffuse bone marrow [99mTc] MIBI uptake were included in the study. All patients underwent whole body scintigraphy at 10 and 60 minutes after i.v. injection of 555 MBq of [99mTc] MIBI. [99mTc] MIBI washout was measured, after decay correction, as: (10 minute counts/pixel minus 60 minute counts/pixel) divided by 10 minute counts/pixel, computed on a region of interest drawn on the thoracic spine (posterior projection), taking care of avoiding heart and splanchnic organs. Disease restaging was performed at a mean time of 32+/-20 months, and patients were considered to be in remission (complete or partial) or to show disease progression on the basis of a complete clinical and hematological evaluation. RESULTS:Patients showing disease progression at restaging (n=26) had higher washout (19.3+/-9.8% vs 12.8+/-6.9%, p<0.05) than patients in remission (n=14). Disease free survival was significantly better in patients with lower washout of [99mTc] MIBI. No differences in therapeutic regimen and stage of disease at admission were found between the 2 groups. When patients treated with melphalan were excluded from the analysis, 87.5% of patients in remission had low washout. CONCLUSIONS: The present study suggests a potential role of [99mTc] MIBI washout in predicting response to chemotherapy in patients with MM.