Trastuzumab therapy duration in HER2-positive de novo metastatic breast cancer: 1999-2018.

Purpose: The optimal duration of first-line trastuzumab (T) treatment for de novo stage IV HER2-positive metastatic breast cancer (MBC) patients after complete response (CR) is not known.

Methods: A retrospective cohort study of de novo stage IV HER2-positive MBC patients who had trastuzumab included in their initial treatment (n = 69), 1999-2018, was conducted with follow-up for CR, progressive disease (PD), vital status, and disease-specific survival (DSS). Statistics included Kaplan-Meier plots and Cox proportional hazards models.

Results: Mean trastuzumab treatment time was 4.1 years (range 0.1-15). 54% of patients experienced CR at average time 9 months on treatment (n = 37). Eight CR patients discontinued T treatment after 18 months average post-CR time (range 0-86) and twenty-nine stayed on T treatment post CR [average 65 months (range 10-170)]. Average follow-up was 6 years, range 1-15 years. 5-year DSS was 92% for CR on T patients (N = 29); 88% CR off T (n = 8); 73% No CR on T (n = 14); and 29% No CR off T (n = 18) (p < 0.001). In forward Cox proportional hazards modeling, CR = yes [HzR = 0.31, (95% CI 0.14, 0.73), p = 0.007], continuous T treatment > 2 years [HzR = 0.24, (95% CI 0.10, 0.62), p = 0.003], and age < 65 [HzR = 0.29, (95% CI 0.11, 0.81), p = 0.018] were significantly associated with better DSS.

Conclusion: Maximum trastuzumab treatment time to CR was 27 months with 2 or more years trastuzumab treatment independently associated with better survival. Survival comparisons and hazard modeling both indicate as good or better survival associated with continuous trastuzumab treatment regardless of CR status. Word count (n = 250).