New findings presented at the 2025 San Antonio Breast Cancer Symposium suggest that early magnetic resonance imaging assessment during neoadjuvant therapy may help predict pathologic complete response and long-term outcomes in patients with triple negative breast cancer receiving pembrolizumab.
Investigators from Parc Taulí Hospital Universitari in Spain assessed the predictive value of MRI response in patients receiving novel neoadjuvant chemotherapy regimen including pembrolizumab, and its correlation with pathologic complete response.
Evaluating MRI timing during neoadjuvant therapy
The retrospective study included 162 patients with stage II-III triple negative breast cancer treated with neoadjuvant chemotherapy between 2000 and 2024. Patients received anthracycline and taxane-based regimens, with one cohort also receiving pembrolizumab. MRI scans were performed at baseline, mid treatment, and before surgery to assess radiologic complete response. Radiologic complete response was defined as no/minimal enhancement compared to normal tissue and pathologic complete response was defined as the absence of invasive tumor in breast and axilla.
Early MRI response correlates with pCR
Overall, the pathologic complete response rate was 44.4% across the full cohort. Rates were significantly higher in the pembrolizumab treated cohort at 68.2%, compared with 40.7% in patients treated with chemotherapy alone.
Early radiologic complete response on MRI was observed in 28.6% of patients overall and was significantly more common among those receiving pembrolizumab (66.6% vs 22.7%). Among patients who achieved early radiologic complete response, 84.1% went on to achieve pathologic complete response. By contrast, patients without early MRI response had substantially lower pCR rates. Final radiologic complete response rates were higher but showed weaker correlation with pathologic outcomes, suggesting that earlier imaging may be more informative for predicting response.
Strong association with long term outcomes
Early MRI response was also associated with improved survival. Patients achieving pathologic complete response had significantly higher overall survival (98.5% vs 66.5%) and event free survival (96.7% vs 64.4%) at five years compared with non-responders. Similar survival advantages were seen among patients with early radiologic complete response, regardless of final imaging findings. At five years, overall survival was 100% patients with early MRI response, compared with 71.6% among those without early response.
Clinical implications
The investigators concluded that early MRI during neoadjuvant pembrolizumab based therapy is a strong predictor of both pathologic complete response and long-term outcomes in triple negative breast cancer. Early radiologic complete response may serve as a non-invasive biomarker to guide treatment decisions, including potential de-escalation strategies in patients at higher risk for treatment related toxicity.
Reference
Taulí P et al. Impact of early magnetic resonance imaging assessment on prediction of pathologic complete response and long-term outcomes in triple negative breast cancer treated with neoadjuvant pembrolizumab. Abstract PD6-02-01. SABCS 2025; 9-12 December.
