Favourable long-term outcomes in selected HER2-Positive early breast cancer patients without pathological complete response after neoadjuvant chemotherapy and trastuzumab: A pre-T-DM1 era cohort study.

[BACKGROUND] Adjuvant trastuzumab emtansine (T-DM1) is the standard treatment for HER2-positive early breast cancer (EBC) patients who do not achieve a pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC). Given the heterogeneity within this population, we analyzed long-term outcomes in non-pCR HER2-positive EBC patients who received adjuvant trastuzumab prior to the availability of the KATHERINE trial results METHODS: This single-center cohort study included all HER2-positive EBC patients treated with neoadjuvant chemotherapy at our hospital between 2006 and 2017. Kaplan-Meier and multivariable Cox regression models were employed to assess long-term invasive disease-free survival (iDFS) and overall survival (OS).

[RESULTS] This study included 103 patients, of which 67.0 % had a residual tumor size of ypT1, and 57.3 % had no residual tumor in the lymph nodes. The median follow-up was 9.3 years. At 3, 5, and 7 years, the iDFS rates were 78.3 %, 72.2 %, and 69.7 %, and the overall survival rates were 90.2 %, 83.3 %, and 79.8 %, respectively. Multivariate analysis identified ypT<2, ypN0, and estrogen receptor positivity as independent predictors of improved iDFS. Among patients with ypT<2, ypN0, and estrogen receptor-positive disease (34 out of 72 with estrogen receptor positivity), iDFS rates were notably high: 97 % (95 % CI: 91.3-100) at 3 years, and 90.9 % (95 % CI: 81.6-100) at both 5 and 7 years.

[CONCLUSION] Patients without a pathologic complete response after neoadjuvant chemotherapy plus trastuzumab represent a heterogeneous group. Those with ypT<2, ypN0, and ER-positive residual disease may still achieve excellent iDFS and OS despite absence of adjuvant T-DM1.