Rationale and objectives: The purpose of the study was to evaluate the hypothesis that magnetic resonance imaging (MRI) and positron emission tomography (PET) are complementary and valuable in monitoring response and assessing residual disease of locally advanced breast cancer (LABC) treated with neoadjuvant chemotherapy. We sought to determine if the combination of the two modalities was more accurate than either alone and could provide better guidance in patient management.
Materials and methods: Sixteen lesions in 15 women with LABC were evaluated with MRI, PET, and clinical breast examination (CBE) before and after neoadjuvant chemotherapy. The pre- and posttherapy maximal tumor sizes on MRI and CBE and standard uptake values (SUVs) on PET served as the measurements for clinical response classification and residual disease assessment. Pathologic assessment provided the reference for macroscopic and microscopic pathologic tumor response and residual disease.
Results: PET correctly predicted lack of pathologic response in five of six cases (83%); CBE predicted correctly in one of six (17%) cases, and MRI predicted correctly in zero of six cases. When PET predicted response, MRI defined the extent of macroscopic pathologic residual disease accurately in 9 of 10 cases (90%). When posttherapy MRI showed complete response (CR) in eight cases, macroscopic pathologic complete response (mCR) was observed in all eight cases (100%).
Conclusion: Our study suggests that combined use of MRI and PET is complementary and offers advantages over CBE. PET was more accurate in predicting pathologic nonresponse. Complete response by MRI correlated well with macroscopic pathologic complete response.