Oral Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2023

Real world analysis of breast cancer patients qualifying for adjuvant CDK4/6 inhibitors (#30)

Yada Kanjanapan 1 2 , Wayne Anderson 3 , Mirka Smith 3 , Jenny Green 3 , Elizabeth Chalker 3 , Paul Craft 1 2
  1. Department of Medical Oncology, Canberra Hospital, Canberra, ACT
  2. Australian National University, Canberra
  3. Epidemiology Section, Data Analytics Branch, ACT Health Directorate, Canberra

Introduction

Treatment intensification with adjuvant CDK4/6 inhibitors has improved disease-free survival, in monarchE and NATALEE trials with abemaciclib and ribociclib respectively, using different eligibility criteria. We assessed the proportion of breast cancer patients represented with these criteria, and their outcome, in an Australian population.

 

Methods

Consecutive patients from ACT Breast Cancer Treatment Group (6/1997 – 6/2017) were analysed. Patients eligible for monarchE had >=4+ lymph nodes (LN) or 1-3+ LN plus tumour >=5cm or grade 3. NATALEE additionally included LN-negative >5cm, and 2.1–5cm grade 3 cancers. Groups were compared by Chi-square testing; survival estimated by Kaplan-Meier method.

 

Results

Of 3840 hormone receptor-positive HER2-negative breast cancer patients, 718 (18.7%) qualified monarchE criteria; 2024 (52.7%) were NATALEE-eligible. monarchE-eligible patients were younger (median 56 versus 59 years, p<0.001), with higher proportion premenopausal (34% versus 22%, p<0.001). Significantly more monarchE-eligible patients received chemotherapy (81% versus 33%, p<0.001). Median overall survival was shorter for monarchE-eligible patients (61 versus 105 months, HR 1.89, 95%CI 1.60 – 2.22, p<0.001).

 

NATALEE-eligible patients were more likely premenopausal with higher chemotherapy-use (66% versus 16%) than non-eligible patients. Node-negative patients comprised 31% of the NATALEE-eligible cohort, while 26% of LN-negative patients qualified for NATALEE. Survival among NATALEE-eligible patients was inferior to non-eligible patients, median 78 versus 106 months (HR 1.36, 95%CI 1.16 – 1.59, p<0.001).

 

Among NATALEE-eligible patients, 65% (n=1306), or 34% of study population, did not qualify for monarchE. Patients eligible for both study criteria had inferior survival to NATALEE-eligible-only patients (median 61 vs 96 months, HR 1.78, 95%CI 1.47 – 2.14, p<0.001).

 

Conclusions

Both trial criteria effectively identified high-risk patients for treatment escalation. monarchE selected the highest risk subgroup with the poorest survival. NATALEE identified an additional 34% of hormone receptor-positive breast cancer patients (26% of LN-negative population) eligible for adjuvant CDK4/6 inhibitor therapy, although absolute benefits maybe smaller given lower baseline risk compared with the monarchE population.

  1. Johnston, S. R., Harbeck, N., Hegg, R., Toi, M., Martin, M., Shao, Z. M., ... & Rastogi, P. (2020). Abemaciclib combined with endocrine therapy for the adjuvant treatment of HR+, HER2−, node-positive, high-risk, early breast cancer (monarchE). Journal of Clinical Oncology, 38(34), 3987.
  2. Slamon, D., Stroyakovskiy, D., Yardley, D. A., Huang, C. S., Fasching, P. A., Crown, J., ... & Hortobagyi, G. N. (2023, June). Ribociclib and endocrine therapy as adjuvant treatment in patients with HR+/HER2− early breast cancer: primary results from the Phase III NATALEE trial. In American Society of Clinical Oncology Annual Meeting.