Background: MRI is the most accurate imaging modality for predicting complete pathological response (pCR) following neoadjuvant chemotherapy (NAC). However, residual disease in pathology specimens has been reported in up to 30% of cases whose MRI showed complete response (MR-CR), necessitating surgery to accurately demonstrate pCR. Treatment of HER2+ disease includes chemotherapy and biological therapy with Herceptin (HC). More recently, a new biological drug, Pertuzumab (Perjeta), has been added to the protocol (HPC) resulting in increased pCR rate. The purpose of this study is to evaluate the ability of MRI to accurately predict pCR in patients with HER2 + disease receiving Pertuzumab as part of their NAC protocol in comparison to those who did not receive the drug.
Patients and Methods: This retrospective study included 39 patients who underwent NAC for HER2+ disease. 18 patients received chemotherapy and Herceptin (HC) and 21 received the same with the addition of Pertuzumab (HPC). Pre-op MRI examinations were reviewed and categorized for residual disease: complete response (MR-CR), partial response (MR-PR) or no response. These findings were compared to pathological response as reported in the surgical pathology report. Statistical evaluation was performed using the Fisher`s exact test
Results: Patient age (average 47 years) was similar in both groups. In the HC group, 33% (6/18) demonstrated pCR and 67% (12/18) had residual disease on pathology; with similar results for MR response assessment in this group. In the HPC group the rate of pCR was higher 57% (12/21) and 43% (9/21) had residual disease on pathology. MR-CR was seen in 52% (11/21) and MR-PR in 43% (9/21), one case (5%) showing no response to treatment on MRI. Correlation between MR assessment and pathology results was similar in both groups showing concordance in 83% for the HC group and 86% for the HPC group. The average size of MR residual disease was smaller in the HPC group: 1 cm vs 1.8cm. MRI falsely estimated residual disease in 2 patients in each group. When MRI predicted no residual disease (MR-CR), disease was present on pathology in 1/18 patients (5.5%) in the HC group and 1/21 patients (4.8%) in the HPC group.
Conclusion: MRI prediction of pathological response is accurate in patients with HER2+ breast cancer, missing residual disease in only 5% of patients. MRI prediction is similar regardless of the addition of Pertuzumab to the treatment protocol.
