Trastuzumab in breast cancer metastatic setting: a retrospective study of clinical predictors of exceptional responders

Background Currently,human epidermal growth factor 2(HER2)-positive, metastaticbreast cancer is considered an incurable disease;however, a small group can remain in long-term remission with theuse of anti-HER2 treatment. This small group of exceptional responders may beclinicallycured. Aim In this retrospectivecohort study, the aim was to identifythe rate of exceptional respondersto trastuzumab-based therapyand potentialclinical predictive factorsin a consecutive cohortof patients with HER2metastatic breast cancer. Methods Electronic medical records from 148patients with HER2-positive metastatic breast cancer that had received trastuzumab as a first line treatmentwereretrospectively evaluated.The patients included had been treated at three different hospitals in Sweden between 2010-2018. Results In total, 24 patients (16.2%; 95% Confidence Interval (CI): 10.9 –23.4%) were classified as exceptional responders to trastuzumab-based therapy. Two clinical factors were potentially associated to exceptional responses: complete remission as best response in 1st line treatment was associated to higher probability (Odds Ratio (OR): 7.67; 95% CI: 2.63 -22.33);presence of lymph node metastases with lower probability for exceptional response (OR: 0.35; 95% CI: 0.11 -1.09) Conclusion -A meaningful number of patients with HER2-positive metastatic breast cancer are expected to be exceptional responders to trastuzumab-based therapy. The achievementof CRis an important predictive factor for exceptional responses. Additional studies preferably with a uniformand widely accepted definition of exceptional responses are warrantedto confirm our findings and further investigate potential clinical and molecularpredictors