Abstract P2-08-23: A population-based study examining the epidemiology, treatment patterns and resource utilization by stage in Ontario patients with HER2+ breast cancer
Authors: Brezden-Masley Christine , Fathers Kelly Elizabeth , Coombes Megan , Xue Cloris , Pourmirza Behin , Jerzak Katarzyna J. 
Published: March 2020

Background: Since the discovery of HER2-targeted treatments for HER2+ breast cancer (BC), women with this historically poor-prognosis subtype have benefitted from dramatic improvements in outcome. As treatment algorithms and staging become more personalized, there is increasing value in understanding real-world clinical characteristics of patients, as well as treatment patterns, resource use and outcomes. To our knowledge, no such data currently exist by BC subtype and stage in one single cohort.

Methods: We retrospectively collected data for women aged 18-105 years, residing in Ontario, utilizing the public healthcare system, and diagnosed with invasive BC from Apr 1, 2012 to Mar 31, 2016. Data were extracted from datasets housed by the Institute for Clinical Evaluative Sciences. Women with HER2+ pathology were identified and baseline characteristics, treatment patterns, and healthcare resource use were descriptively compared between stage I-III and stage IV sub-cohorts. Outcomes assessed included 5-year overall survival (OS) rates by stage. Patients alive/lost to follow-up at the end of the study period (Mar 31, 2017) were censored. Unit costs (2017 CAD $) for publicly funded healthcare services were multiplied by resources used in order to calculate total and annual health-system related costs.

Results: In total, 4,889 women were identified as having HER2+ BC; 4535 with stage I-III and 354 with stage IV disease at diagnosis. Patients with stage IV HER2+ BC more frequently had larger or unknown tumour size and lower hormone receptor positivity rates than those with stage I-III tumours. With a median follow-up of 34.1, 33.7, 32.2 and 21.4 mos, 5-year OS rates were 96.5, 87.5, 79.9 and 36.6% for stage I, II, III, and IV, respectively. Surgery was the most common treatment modality in stage I-III (n=4372, 96.4%) and least common in stage IV (n=82, 23.2%). Among patients treated with upfront surgery for early stage disease (n=3451, 78.9%), 3135 (90.8%) received adjuvant systemic therapy (AT) with a median time from surgery to treatment of 42 days (IQR: 26,56). The remaining 921 stage I-III patients (20.1%) received neo-AT starting a median of 28 days (IQR: 21,39) after diagnosis, with 912 (99.0%) also receiving AT. In total, 3521 (77.6%) of patients with stage I-III BC received radiation. Among patients with metastatic HER2+ BC, 314 (88.7%) received systemic therapy and 213 (60.2%) were treated with radiotherapy. Annual mean healthcare cost per person was $54,852.39 for stage I-III and $159,347.97 for stage IV HER2+ BC. In the stage I-III sub-cohort, pharmaceuticals and cancer clinic visits accounted for ~70% of measured resource costs, whereas pharmaceuticals and inpatient hospital services were the main cost contributors for patients with stage IV disease.

Conclusions: Characteristics and clinical outcomes were as expected for our Ontario-based population of women with HER2+ BC. Patients appeared to be treated within reasonable timeframes and in alignment with the strategies recommended by Cancer Care Ontario at the time of the study. Improvements in survival of stage IV HER2+ BC coincide with increased resource utilization, largely driven by systemic therapy and inpatient hospitalization. While there are fewer patients with stage IV HER2+ BC, the annual mean cost per person is nearly three-fold higher than in those with early stage disease, and demonstrates a need for interventions that decrease hospitalizations and/or pharmaceutical treatment costs.

Citation Format: Christine Brezden-Masley, Kelly Elizabeth Fathers, Megan Coombes, Cloris Xue, Behin Pourmirza, Katarzyna J. Jerzak. A population-based study examining the epidemiology, treatment patterns and resource utilization by stage in Ontario patients with HER2+ breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-08-23.