ABSTRACT
Multidrug resistance [MDR], which may be due to the over expression of P-glycoprotein [Pgp] and/or MRP, is a major problem in neoadjuvant chemotherapy of osteosarcoma. The aim of this study was to investigate the role of Tc-99m MIBI scan for predicting the response to pre-operative chemotherapy. Twenty-five patients [12 males and 13 females, aged between 8 and 52y] with osteosarcoma were studied. Before the chemotherapy, planar [99m]Tc-MIBI anterior and posterior images were obtained 10-min [tumor-to-background ratio: [T[1]/B[1]][10min]] and 3-hr after tracer injection. After completion of chemotherapy, again [99m]Tc-MIBI scan was performed at 10-min after tracer injection. In addition to calculation of decay corrected tumor to background [T/B] ratios, using the 10-min and 3-hr images of the pre-chemotherapy scintigraphy, percent wash-out rate [WR%] of [99m]Tc-MIBI was calculated. Using the 10-min images of the pre- and post-chemotherapy scans, the percent reduction in uptake at the tumor site after treatment [Red%] was also calculated. Then after surgical resection, tumor response was assessed by percentage of necrosis. All patients showed significant [99m]Tc-MIBI uptake in early images. Only 9 patients showed good response to chemotherapy [necrosis >/= 90%] while 16 patients were considered as non-responder [necrosis <90%]. There was no statistical significant difference between non-responders and responders in [T[1]/B[1]] [10min].There was a significant negative correlation between WR% and percentage of necrosis [P=0.001]. On the other hand, there was a significant correlation between Red% and percentage of necrosis [P<0.001].There was also statistical significant difference in WR% and Red% between non-responders and responders [both P< 0.001]. Washout rate of [99m]Tc-MIBI in pre-chemotherapy scintigraphy as well as Red% using pre- and post-chemotherapy MIBI scintigraphy are useful methods for predicting response to neoadjuvant chemotherapy