Washout of [99mTc] sestamibi in predicting response to chemotherapy in patients with multiple myeloma

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.

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.

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.

The present study suggests a potential role of [99mTc] MIBI washout in predicting response to chemotherapy in patients with MM.