Breast cancer phenotype influences MRI response evaluation after neoadjuvant chemotherapy.

Purpose: To evaluate which factors may influence magnetic resonance imaging (MRI) performance in the detection of pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC).

Method: This retrospective study included 219 patients diagnosed with invasive breast carcinoma who underwent breast MRI before and after NAC. The MRI findings were compared to gold standard pathological examinations. Resolution of invasive breast disease was defined as pCR.

Results: The mean age of our cohort was 48 years (range: 20-85). The molecular subtypes included: Luminal B/Her-2 negative (n = 89; 40%), triple-negative (n = 69; 32%), Luminal B/Her-2 positive (n = 43; 20%), and Her-2 overexpression (n = 18; 8%). MRI analysis after NAC showed complete response in 76 cases (35%), while pathological analysis of surgical specimens after NAC detected pCR in 85 cases (39%). The accuracy of MRI in diagnosing pCR was 80%, with 69% sensitivity, 87% specificity, and positive and negative predictive values of 78% and 82%, respectively. The only factor statistically associated with a higher discordance rate between MRI and pathologic response was the presence of non-mass enhancement at pre-treatment MRI (p = 0.003).

Conclusions: MRI demonstrated good accuracy in predicting pCR after NAC among the breast cancer patients examined. However, non-mass enhancement at pre-treatment MRI negatively affected the diagnostic performance of MRI in assessing treatment response after NAC.