Adjuvant Trastuzumab with or without Chemotherapy in Stage 1 pT1N0 HER2+ Breast Cancer: A National Cancer Database Analysis

Purpose: Approximately 20% of all breast cancers (BC) are HER2 amplified. In the APT trial, weekly paclitaxel/ trastuzumab in node negative HER2+ BC with tumors Methods: In the National Cancer Database (2004-2017), patients with a primary diagnosis of pT1N0M0 HER2+ BC, were separated into two groups: (i) HER2 monotherapy, i.e. trastuzumab, and (ii) chemo-HER2 therapy. A 3:1 propensity match was performed to balance patient selection bias between the two different cohorts. Long-term overall survival (OS) was compared between both groups. Results: A total of 23, 281 patients met the criteria. 22,268 (96.7%) received chemo-HER2 therapy and 1,013 (4.4%) received HER2 monotherapy. Propensity match identified 1,995 patients who received chemo-HER2 therapy, and 666 who received HER2 monotherapy. After match, adjuvant chemo-HER2 therapy was associated with a modest survival advantage over HER2 monotherapy (5-year OS 94.1% vs. 90.6%, P=0.041). Conclusions: Even though there is a modest OS advantage favoring adjuvant chemo-HER2 therapy in pT1N0 HER2+ BC, HER2 monotherapy was associated with 5-year OS >90%. Therefore, in select patients who have contraindications for cytotoxic chemotherapy, or decline adjuvant chemotherapy, adjuvant trastuzumab monotherapy appears to be a reasonable alternative.