115PPathological complete response rates following neoadjuvant systemic therapy in 300 patients with early or locally advanced HER2 positive breast cancer: The Royal Marsden experience

Background: Neoadjuvant chemotherapy plus anti-HER2 treatment is increasingly becoming the treatment of choice for all but the lowest risk HER2+ early and locally advanced breast cancer (BC). Patients achieving a pathological complete response (pCR) have substantially better outcomes compared with non-pCR. We evaluated the pCR rates following neoadjuvant systemic therapy in our HER2+ BC population and determined the influence of tumour and patient characteristics, and adverse events on pCR rates, disease free survival (DFS) and overall survival (OS). Methods: We retrospectively identified patients with early and locally advanced HER2+ BC who received neoadjuvant treatment from January 2013 to December 2017 and underwent subsequent surgery. pCR was defined as ypT0/is N0. Demographics, patient and disease characteristics, pathological responses, toxicities, dose delays and reductions were recorded. Statistical analysis was undertaken using Chi-squared, Kaplan Meier and Log-rank tests. Results: 300 patients were identified. Median age was 51 years (range 25-78) and 286 (95.3%) patients had performance status (PS) 0. 11 (4.0%) patients had clinical stage I, 189 (63.0%) stage II and 100 (33.0%) stage III disease. 204 (68.0%) had grade 3 disease and 282 (94.0%) ductal histology. 185 (61.7%) patients had ER+ disease and 115 (38.3%) ER- disease. 155 (52.0%) patients were treated with chemotherapy plus Trastuzumab. 143 (48.0%) patients had chemotherapy plus Trastuzumab and Pertuzumab. pCR rate in the overall population was 54.3% and significantly better in the ER- compared with the ER+ subgroup (68.7 vs 45.4 %; p < 0.001). Patients on dual anti-HER2 blockade achieved higher pCR rates compared with those on Trastuzumab (56.6 vs 52.2%) although the difference was not statistically significant (p = 0.448). pCR rates were not influenced by age, PS, dose reductions or dose delays but were significantly lower in case of chemotherapy early discontinuation. With a median follow-up of 23 months, median DFS and OS were not reached. Conclusions: In our analysis, pCR rate was similar to published data in the literature and was higher in the ER-/HER2 positive subgroup. Legal entity responsible for the study: The Breast Unit, The Royal Marsden Hospital. Funding: Has not received any funding. Disclosure: All authors have declared no conflicts of interest.