Real-world outcomes of early-stage HER2-positive breast cancer patients treated with adjuvant paclitaxel and trastuzumab

Weekly paclitaxel and trastuzumab (APT regimen) represents the standard treatment for most stage I HER2+ breast cancer (BC) patients based on results of the single arm phase II APT trial. Confirmation of long-term outcomes in real-world cohorts is of interest. This retrospective study included patients with early HER2 + BC (pT ≤ 3 cm; pN0/N1mic) treated with APT regimen. This study included 276 patients; most presented hormone receptor (HR) positive (75%, N = 207) and grade 3 tumors (65.6%, N = 181). The majority had pT ≤ 2 cm (92.4%, N = 255), no nodal involvement (93.1%, N = 257), with only 19 patients (6.9%) presenting N1mic. Anatomical stage was: IA 86.2% (N = 238), IB 6.2% (N = 17), and IIA 7.6% (N = 21). At a median follow-up of 4.4 years, 3-year recurrence free survival (RFS) was 97.3% (95% CI 95.1-99.5), 3-year distant relapse free survival (DRFS) was 98.2% (95% CI 96.4-100), and 3-year invasive breast cancer free survival (IBCFS) rate was 97.1% (95% CI 94.7-99.5). A statistically significant difference in RFS was observed according to anatomical stage ( p < 0.001). This real-world study confirms that APT regimen is associated with excellent outcomes in stage IA HER2 + BC patients, while caution is warranted for patients with stage IB or IIA disease.