RESUMO
PURPOSE: Numerous non-invasive imaging methods for evaluating the chemotherapy response of breast cancer patients are currently being explored. The aim of present study was to investigate whether the washout rates (WRs) of 99mTc-MIBI could predict the response to chemotherapy in patients suffering with infiltrating ductal carcinoma using the expressions of multidrug resistance-related protein (MRP) and P-glycoprotein (Pgp). METHODS: From May 2002 and March 2004, the patients were randomly and consecutively selected according to the results of immunohistochemical analyses of breast carcinoma specimens before the administration of neoadjuvant chemotherapy. A total 45 infiltrating ductal carcinomas in 45 female patients were selected and they were separated into three groups: group A consisted of tumors with both negative Pgp and MRP expressions (n=15); group B consisted of the tumors that were positive for either a Pgp expression or a MRP expression (n=15); group C consisted of the tumors that were positive for both Pgp and MRP expressions (n=15). All the patients were referred for double phase 99mTc-MIBI mammoscintigraphy after the injection of 925 MBq of 99mTc-MIBI to calculate the WR. The tumor response was evaluated after completion of neoadjuvant chemotherapy. The tumor response was classified as a complete or partial response (the responder group) and stable or progression (the non-responder group). All the patients underwent surgery. RESULTS: The response rate of group C was lower than that of the other groups, but the difference was not statistically significant (p=0.283). The WR of non-responder group was lower than that of the responder group, although the difference was not statistically significant (p=0.674). The washout rates of group C was the highest than other groups and the difference was statistically significant (p=0.001). CONCLUSION: In conclusion, the WR of 99mTc-MIBI is helpful for in vivo determination of both the Pgp and MRP expressions for infiltrating ductal carcinoma of the breast.