Trastuzumab without chemotherapy in the adjuvant treatment of breast cancer: subgroup results from a large observational study

Background: The topic of trastuzumab therapy without chemotherapy in early breast cancer (EBC) has been repeatedly discussed at international consensus meetings, but is compromised by the lack of solid evidence from clinical studies. Methods: An observational study database of patients with EBC receiving trastuzumab-containing (neo) adjuvant therapy was screened to identify those patients who did not receive cytostatic agents. Results: Of 3935 patients, 232 (6%) were identified who received no chemotherapy, being characterized by older age, worse performance status, and/or less aggressive histology. Relapse-free survival in this cohort was 84% (95% confidence interval [CI] 78-89%) at 3 years and 80% (95% CI 74-87%) at 5 years. However, these rates were significantly worse than those in the group of patients who received chemotherapy (hazard ratio 1.49; 95% CI 1.06-2.09; P = 0.022). A similar pattern was observed for overall survival, with marginally non-significant inferiority in the group receiving no chemotherapy (hazard ratio 1.56; 95% CI 1.00-2.44; P = 0.052). Survival rates in patients receiving no chemotherapy were 93% (95% CI 88-97%) and 87% (95% CI 81-93%) at 3 and 5 years, respectively. These findings were confirmed by a propensity score analysis accounting for selection bias. Conclusions: Trastuzumab plus chemotherapy should remain the preferred option in all patients with HER2-positive EBC with an indication for adjuvant treatment. However, a limited proportion of patients will need an alternative treatment approach, either because of contraindications or the patient's preference. In these selected patients, trastuzumab monotherapy, eventually combined with endocrine agents, might be a reasonable option offering favorable long-term outcomes by addressing the high-risk profile associated with HER2-positive disease.