A new study has reported that magnetic resonance imaging (MRI) during neoadjuvant chemotherapy to monitor response to treatment is effective in triple negative and HER2 positive disease but is inaccurate in estrogen receptor positive/HER2 negative breast cancer. The study was designed to investigate the relevance of breast cancer subtypes for MRI monitoring of response to chemotherapy that is given before breast surgery to remove the tumor. The study included 188 women who underwent breast MRIs before and during neoadjuvant chemotherapy.

The breast cancers were grouped into three subtypes: triple negative (estrogen receptor negative, progesterone receptor negative and not human epidermal growth factor receptor 2 overexpressing (ER-/PR-/HER2-)), HER2 overexpressing (HER2+), and ER+/HER2- (the most common breast cancer subtype). Response to treatment was determined by the presence or absence of residual tumor in the breast tissue removed during surgery after completion of chemotherapy. At the same time, a continuous scale (the breast response index) was used to measure the relative change in tumor stage.

Residual breast cancer (as determined by pathology after surgery) was found in 31 of 47 (66%) triple negative tumors, 23 of 38 (61%) HER2 positive tumors, and 96 of 103 (93%) ER+/HER2 negative tumors. Multivariate analysis of residual disease found significant associations between breast cancer subtype and MRI assessments. The breast response index also showed significant correlation between breast cancer subtype, MRI, and age for triple negative and HER2 positive tumors. Residual tumor after neoadjuvant chemotherapy in the triple negative and HER2 positive group was found to be significantly associated with change during neoadjuvant chemotherapy as measured by MRI. On the other hand, no associations were found for ER+/HER2 negative tumors. The authors conclude that MRI during neoadjuvant chemotherapy to monitor response to treatment is effective in triple negative and HER2 positive disease but is inaccurate in ER+/HER2 negative breast cancer.