Outcomes of trastuzumab therapy in HER2-positive early breast cancer patients: extended follow-up of JBCRG-cohort study 01

BACKGROUND: Previous large trials of trastuzumab (TZM) demonstrated improved outcomes in patients with HER2-positive early breast cancer. However, its effectiveness and safety in Japanese patients is not yet clear. Recently, new anti-HER2 agents were developed to improve treatment outcomes, but the patient selection criteria remain controversial. PURPOSE: The aim of this study was to evaluate the long-term effectiveness of TZM therapy as perioperative therapy for HER2-positive operable breast cancer in daily clinical practice and to create a recurrence prediction model for therapeutic selection. METHODS: An observational study was conducted in Japan (UMIN000002737) to observe the prognosis of women (n = 2024) with HER2-positive invasive breast cancer who received TZM for stage I–III C disease between July 2009 and June 2011. Moreover, a recurrence-predicting model was designed to evaluate the risk factors for recurrence. RESULTS: The 5- and 10-year disease-free survival (DFS) rates were 88.9 (95% CI 87.5–90.3%) and 82.4% (95% CI 79.2–85.6%), respectively. The 5- and 10-year overall survival (OS) rates were 96% (95% CI 95.1–96.9%) and 92.7% (95% CI 91.1–94.3%), respectively. Multivariate analysis revealed that the risk factors for recurrence were an age of ≥ 70 years, T2 or larger tumors, clinically detected lymph node metastasis, histological tumor diameter of > 1 cm, histologically detected lymph node metastasis (≥ n2), and the implementation of preoperative treatment. The 5-year recurrence rate under the standard treatment was estimated to be > 10% in patients with a score of 3 or greater on the recurrence-predicting model. CONCLUSION: The recurrence-predicting model designed in this study may improve treatment selection of patients with stage I–III C disease. However, further studies are needed to validate the scores generated by this model. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s12282-020-01057-4) contains supplementary material, which is available to authorized users.