Pre-Operative MRI in HER-2 Receptor Positive and Her-2 Receptor Negative Breast Cancer: A Comparison

Objectives: MRI is the most sensitive modality for local staging of breast cancer. Herceptin receptor over-expression is seen in 15% - 30% of breast tumours, and is associated with increased aggression, poorer prognosis, higher grade at diagnosis and increased lymphatic dissemination. This study aimed at evaluating the role of MRI in Herceptin receptor positive vs negative tumours. Methods: 193 pre-operative MRIs were performed in 2021 for staging of 162 Her-2 negative and 37 Her-2 positive tumours. Recall rates and further biopsies (ipsilateral/contralateral) were assessed in both groups, and MRI largest size was compared to pathological size of invasive cancer and DCIS. Results: 36.4% of Her-2 negative tumours were recalled; further ipsilateral malignancy was identified in 13.6%. Contralateral malignancy was identified in 1.2%. 29.7% of Her-2 positive tumours were recalled; further ipsilateral malignancy was identified in 16.2%. No contralateral malignancy was seen in Her-2 positive tumours. The OR of Her-2 positive tumours having ipsilateral foci of malignancy on MRI is 0.83 (CI 0.3, 2.2). Pathological size concordance with MRI size was seen in 70.3% of Her-2 negative, and 48.6% of Her-2 positive tumours. Discordance in both groups was due to MRI size overestimation (70.8% of Her-2 negative discordance; 89.4% of Her-2 positive discordance). Conclusions: Pre-operative MRI did not detect significant increased additional foci in Her-2 positive tumours. Significant concordance with pathological size was not seen in both groups; MRI overestimation was the most frequent cause for discordance in both groups. Advances in Knowledge: This study compares MRI features of Her-2 positive and Her-2 negative tumours. It demonstrates that there is no significant increased multifocality or multicentricity of Her-2 positive tumours, but MRI over-estimates size in 30% of Her-2 negative and 51% of Her-2 positive cancers.