Magnetic resonance imaging as a predictor of pathologic response in patients treated with neoadjuvant systemic treatment for operable breast cancer. Translational Breast Cancer Research Consortium trial 017

BACKGROUND

Increased pathologic complete response (pCR) rates observed with neoadjuvant chemotherapy (NCT) for some subsets of patients with invasive breast cancer have prompted interest in whether patients who achieved a pCR can be identified preoperatively and potentially spared the morbidity of surgery. The objective of this multicenter, retrospective study was to estimate the accuracy of preoperative magnetic resonance imaging (MRI) in predicting a pCR in the breast.

METHODS

MRI studies at baseline and after the completion of NCT plus data regarding pathologic response were collected retrospectively from 746 women who received treatment at 8 institutions between 2002 and 2011. Tumors were characterized by immunohistochemical phenotype into 4 categories based on receptor expression: hormone (estrogen and progesterone) receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative (n = 327), HR-positive/HER2-positive, (n = 148), HR-negative/HER2-positive, (n = 101), and triple-negative (HR-negative/HER2 negative; n = 155). In all, 194 of 249 patients (78%) with HER2-positive tumors received trastuzumab. Univariate and multivariate analyses of factors associated with radiographic complete response (rCR) and pCR were performed.

RESULT

For the total group, the rCR and pCR rates were 182 of 746 patients (24%) and 179 of 746 patients (24%), respectively, and the highest pCR rate was observed for the triple-negative subtype (57 of 155 patients; 37%) and the HER2-positive subtype (38 of 101 patients; 38%). The overall accuracy of MRI for predicting pCR was 74%. The variables sensitivity, negative predictive value, positive predictive value, and accuracy differed significantly among tumor subtypes, and the greatest negative predictive value was observed in the triple-negative (60%) and HER2-positive (62%) subtypes.

CONCLUSIONS

The overall accuracy of MRI for predicting pCR in invasive breast cancer patients who were receiving NCT was 74%. The performance of MRI differed between subtypes, possibly influenced by differences in pCR rates between groups. Future studies will determine whether MRI in combination with directed core biopsy improves the predictive value of MRI for pathologic response.

MRI staging after neoadjuvant chemotherapy for breast cancer: does tumor biology affect accuracy?

BACKGROUND

A discrepancy often exists between the post-neoadjuvant chemotherapy (NAC) breast tumor size on magnetic resonance imaging (MRI) and pathologic tumor size. We seek to quantify this MRI/pathology discrepancy and determine if the accuracy of MRI post NAC varies with tumor subtype.

METHODS

The University of Pittsburgh Medical Center (UPMC) Cancer Registry and radiology database were searched for patients with breast cancer who underwent NAC and MRI staging between 2004 and 2009. We compared radiologic to pathologic staging and stratified differences based on tumor biology using univariate, multivariate, and receiver operating characteristic (ROC) analysis.

RESULTS

Two hundred three of 592 patients undergoing surgery after NAC for breast cancer had MRI staging pre and post chemotherapy. All patients had intact tumors prior to the initiation of chemotherapy. Average tumor size by MRI was 4.0 cm pre chemotherapy and 1.2 cm post chemotherapy. The average pathologic tumor size was 1.7 cm (range 0-13 cm). The difference between MRI and pathologic tumor size was greatest in luminal (1.1 cm) and least in triple-negative (TN) and human epidermal growth factor receptor 2 (HER2)-positive tumors (<0.1 cm) (p = 0.015). MRI was a good discriminator for pathologic complete response (pCR) [area under the curve (AUC) 0.777]. Its predictive value for pCR was much greater in TN and estrogen receptor(ER)-/HER2+ than in luminal tumors (73.6 vs. 27.3%).

CONCLUSIONS

MRI is an effective tool for predicting response to NAC. The accuracy of MRI in estimating postchemotherapy tumor size varies with tumor subtype. It is highest in ER-/HER2+ and TN and lowest in luminal tumors. Knowledge of how tumor subtype affects MRI accuracy can guide recommendations for surgery following NAC.