Evaluation of Recurrence Rate in Canadian Patients With Stage II/III HR+/HER2- Early Breast Cancer in the Real-World Setting.

Background: Breast cancer is the most prevalent cancer and second leading cause of cancer-related mortality among Canadian women. Most of cases belong to the HR+/HER2- subtype, representing approximately two-thirds of all instances. Objectives: This real-world evidence study aims to comprehensively analyze the treatment pattern, and clinical outcomes of Canadian patients diagnosed with early-stage HR+/HER2- breast cancer. Design: This retrospective, longitudinal cohort study involved 541 patients enrolled in the pan-Canadian cancer patient registry PMT (Personalize My Treatment). Methods: The cohort included patients with newly diagnosed or recurrent stage II or III HR+/HER2- breast cancer between January 1st, 1992, and May 31st, 2022. Summary statistic to describe treatment pattern and Kaplan Meir analysis for clinical outcome were used. Results: In the adjuvant setting, our study found that ET was administered to 75.6% of the cohort, with a significant preference for combining ET with cytotoxic agents and, particularly in stage III patients. In addition, neoadjuvant therapy, primarily using cytotoxic agents, was higher in stage III patients, and those receiving neoadjuvant therapy were more likely to either continue with ET as adjuvant treatment. The median duration of adjuvant ET was 4.5 years. In the adjuvant patient population, recurrence rates progressively increased over time from 13.2% after 2 years, 21.4% after 3 years, 30.3% after 5 years, and peaking at 58.4% after 10 years. Median time to recurrence for the patient population on ET was 7.76 years. OS rate for patients on ET was 94.6% at 5 years and 78.3% at 10 years. Conclusions: This study highlights the high unmet need in stage II and stage III breast cancer, with 1 patient out of 3 recurring after 5 years, and more than half recurring after 10 years despite adjuvant treatment with ET alone. This highlights the need for more effective and tolerable treatment options to address disease recurrence in both the short and long term for eBC HR+/HER2- patients in Canada.