Stage I HER2-Positive Breast Cancer: Long-Term Follow-up of Adjuvant T-DM1

In In The News by Barbara Jacoby

By: Matthew Stenger

From: ascopost.com

In a 5-year update of the phase II ATEMPT trial reported in the Journal of Clinical Oncology, Tarantino et al found that 1 year of adjuvant ado-trastuzumab emtansine (T-DM1) was associated with “outstanding” long-term outcomes in patients with stage I HER2-positive breast cancer.

Study Details

In the multicenter trial, 512 patients who had undergone surgery were randomly assigned 3:1 between May 2013 and December 2016 to receive T-DM1 (3.6 mg/kg once every 21 days for 17 cycles) or paclitaxel/trastuzumab (TH; once weekly paclitaxel at 80 mg/m2 with concurrent once-weekly trastuzumab at a loading dose of 4 mg/kg followed by 2 mg/kg for 12 weeks, followed by 6 mg/kg of trastuzumab once every 21 days for 13 cycles). The analysis population consisted of 383 patients in the T-DM1 group and 114 patients in the TH group who received protocol treatment.

The initial analysis of the trial assessed the efficacy of T-DM1 (no comparison with TH) and compared rates of clinically relevant toxicities between the two groups. The 3-year invasive disease–free survival rate in the T-DM1 group was 97.8%, rejecting the null hypothesis (P < .001), and the clinically relevant toxicity rates were 46% in the T-DM1 group and 47% in the TH group (P = .83).

The current analysis presented efficacy outcomes after a median follow-up of 5.8 years.

Key Findings

Among the 383 patients in the TDM-1 group, 11 had invasive disease–free survival events, representing a 5-year invasive disease–free survival rate of 97.0% (95% confidence interval [CI] = 95.2%–98.7%). At 5 years, the recurrence-free interval was 98.3% (95% CI = 97.0%–99.7%), overall survival rate was 97.8% (95% CI = 96.3%–99.3%), and breast cancer–specific survival rate was 99.4% (95% CI = 98.6%–100%).

The study was not powered to compare efficacy outcomes between the T-DM1 group and the TH group. Among the 114 patients in the TH group, 9 had invasive disease–free survival events, representing a 5-year invasive disease–free survival rate of 91.1% (95% CI = 85.7%–96.8%). At 5 years, the recurrence-free interval was 93.2%, overall survival rate was 97.9%, and breast cancer–specific survival rate was 99.0%.

Among all patients in both groups with HER2DX testing scores (n = 187), the 5-year outcomes were better among those with low-risk vs high-risk tumors, including the recurrence-free interval (98.1% vs 81.8%, hazard ratio [HR] = 0.10, P = .01) and invasive disease–free survival (96.3% vs 81.8%, HR = 0.20, P = .047).

The investigators concluded: “Adjuvant T-DM1 for 1 year leads to outstanding long-term outcomes for patients with stage I HER2-positive breast cancer. A high HER2DX risk score predicted a higher risk of recurrence in ATEMPT.”

Sara M. Tolaney, MD, MPH, of the Breast Oncology Program, Dana-Farber Brigham Cancer Center, Boston, is the corresponding author of the Journal of Clinical Oncology article.