OBJECTIVES: This retrospective study described the incidence and characteristics of female patients in Norway with early breast cancer with high-risk of disease recurrence, who met the high-risk criteria in monarchE (cohort 1), a Ph3 trial of abemaciclib for the adjuvant treatment of HR+, HER2-, node-positive, high-risk, early breast cancer.

METHODS: Data from female patients with HR+, HER2-, Stage I-IIIC breast cancer, diagnosed between 2010-2019 and who had surgery were obtained from the Norwegian Breast Cancer Register. High-risk of recurrence was defined as per monarchE trial (cohort 1) criteria: having ≥4 positive lymph nodes or 1–3 positive nodes and grade 3 and/or primary tumor size ≥5cm. Patients not meeting this criteria were classified into low/moderate risk group. Survival rate was estimated using Kaplan-Meier curve.

RESULTS: 20,632 female patients were included. 2,624 of them (12.7%) met the inclusion criteria for high risk of recurrence, 17,637 (85.5%) were considered low/moderate risk, while the rest were unknown (1.8%). Mean cases per year for the high-risk population was 262 (SD 22.9), and for the low/moderate risk 1,764 (SD 269.5). Majority of patients with stage III cancer were high-risk (78.9% of all stage IIIA/IIIB (n=1083) and 91.8% (n=302) for stage IIIC. In the high-risk population, 34.4% (n=908) had 1-3 positive lymph nodes (LN) and 65.6% (n=1721) ≥4 LN. The majority had tumor Grade 2 (40.1%; n=1,051) or 3 (40.5%, n=1,062) and a tumor size ≥2- <5cm (54.2%, n=1422) or ≥ 5cm (21.2%, n=557). 5-year overall survival rate was significantly lower for high-risk compared to low/moderate risk population (83.5% vs 94.3%; p<0.0001).

CONCLUSIONS: About 13% of female patients with HR+, HER2-, Stage I-IIIC breast cancer in Norway diagnosed between 2010 and 2019 met the inclusion criteria for cohort1 high-risk of recurrence used in the monarchE trial and could benefit from more effective adjuvant treatments.