This study evaluated the role of (99m)Tc-sestamibi washout in the prediction of pathologic tumor response to neoadjuvant chemotherapy in 30 patients with locally advanced breast cancer.
Methods: Two (99m)Tc-sestamibi studies were performed before and after chemotherapy for each patient. Early (10 min) and delayed (240 min) planar breast views were acquired after a 740-MBq (99m)Tc-sestamibi intravenous injection, and the washout rate (WOR) was computed. All patients underwent radical mastectomy with pathologic evaluation of the residual tumor size.
Results: The pretherapy (99m)Tc-sestamibi WOR ranged from 14% to 92% (mean +/- SD, 50% +/- 18%). At pathologic examination, 15 patients showed no tumor response to chemotherapy and 15 patients showed an objective response to chemotherapy. The pretherapy (99m)Tc-sestamibi study predicted chemoresistance (WOR > 45%) in 18 of 30 patients and no chemoresistance (WOR < or = 45%) in 12 of 30 patients. When the WOR cutoff was set at >45%, the prognostic performance of the test was indicated by a sensitivity of 100%; a specificity of 80%; positive and negative predictive values of 83% and 100%, respectively; and a likelihood ratio of 5. The repeatability of the test was good, with 80%-93% interreader agreement (kappa = 0.57-0.85). Posttherapy (99m)Tc-sestamibi studies confirmed the pretherapy study prediction in 29 of 30 patients.
Conclusion: (99m)Tc-Sestamibi WOR is a reliable test for predicting tumor response to neoadjuvant chemotherapy. In fact, negative findings (WOR < or = 45%) rule out chemoresistance and positive findings (WOR > 45%) indicate a high risk of chemoresistance.