Characteristics, healthcare utilization, and outcomes of patients with HER2-low breast cancer.

PURPOSE: Treatment for HER2-low [defined as ImmunoHistoChemistry (IHC) 1 + or 2 + and negative/normal in Situ Hybridization (ISH)] breast cancer patients is rapidly evolving, yet we lack critical information about the HER2-low population. METHODS: We conducted a retrospective cohort study of women aged 18 years or older diagnosed with breast cancer between 2010 and 2016 in North Carolina. Analyses were conducted for the overall cohort and a stage IV sub-cohort. We examined demographic and clinical characteristics, and characterized prevalence of HER2-low disease and healthcare utilization. We estimated adjusted rate ratios for the association between HER2 classifications and utilization outcomes, and hazard ratios for 3-year all cause mortality (stage IV only). RESULTS: The overall and stage IV cohorts included 12,965 and 635 patients, respectively. HER2-low patients represented more than half of both cohorts (59% overall, 53% stage IV). HER2-low patients were more likely than IHC 0 patients to have hormone receptor (HR)-positive disease. In the stage IV cohort, HER2-low patients were more likely to be Black (26% vs. 16% IHC 0, p = 0.0159). In both cohorts, rates of hospitalizations were slightly higher among HER2-low patients. There were no survival differences between HER2-low and IHC 0 among stage IV patients. CONCLUSION: New treatment options for HER2-low breast cancer may have potential for significant impact at the population level particularly for patients with stage IV disease. In light of racial differences between HER2-low and IHC 0 patients observed in our cohort, research- and practice-based efforts to ensure equitable adoption of new treatment guidelines for patients with HER2-low metastatic breast cancer will be essential.

A real-world study of treatment sequences and second-line clinical outcomes in patients with HER2-positive metastatic breast cancer in US community practice.

PURPOSE: Standard-of-care for HER2-positive metastatic breast cancer (HER2 + mBC) patients consists of trastuzumab ± pertuzumab with chemotherapy in first-line (1L), and ado-trastuzumab emtansine (T-DM1) or the more recently approved trastuzumab deruxtecan (T-DXd) in second-line (2L). Contemporary data on treatment sequencing and real-world effectiveness is limited. This study aims to report 2L treatments and outcomes among HER2 + mBC patients in the United States (US). METHODS: HER2 + mBC patients initiating 2L treatment (index date) between January 2014 and February 2021 were identified from the Syapse Learning Health Network (LHN) database. Summary statistics for patient characteristics, treatment received, reasons for 2L discontinuation and time to 2L-clinical outcomes are reported. RESULTS: Of the 312 patients initiating 2L treatment, had a median age of 59 years (interquartile range [IQR], 50-66) at the start of 2L. The majority were white (69%) and had de novo mBC (62%). Top three 2L regimens included T-DM1 ± endocrine therapy (29%), trastuzumab/pertuzumab/taxane (10%) and T-DM1/trastuzumab (8%). Around 88% discontinued 2L and 63% received subsequent treatment. Median time-to-next-treatment was 10.6 months (95% CI, 8.8-13.3) and real-world progression-free-survival was 7.9 months (95% CI, 7.0-9.9). Among 274 patients who discontinued 2L, 47% discontinued due to progression and 17% because of intolerance/toxicity, respectively. CONCLUSION: This real-world US study showed that approximately two-thirds of 2L patients received subsequent therapy and disease progression was the most common reason for 2L discontinuation highlighting the need for timely 2L treatment with the most efficacious drug to allow patients to achieve longer treatment duration and delayed progression.