Anti-Her2 therapy patterns in metastatic breast cancer-Real-world data suggest undertreatment

Abstract

Treatment efficacy of anti-HER2 therapies for metastatic breast cancer (mBC) has been demonstrated in clinical trials, but real-world data are lacking. In particular, it is unclear whether patients in clinical practice receive treatment as recommended. We took advantage of population-based registries in Norway to assess anti-HER2 therapy patterns in real-world data, with specific attention to the treatment of vulnerable groups. We included 715 patients with HER2+ mBC diagnosed from 2012 to 2021. Median age was 60 years, 473 (66%) had relapsed from early-stage BC, and 440 (62%) had hormone receptor positive (HR+) disease. Anti-HER2 therapy patterns aligned with national recommendations. Median treatment duration for first line therapy was 7.2 months, where 261 patients (55%) used trastuzumab and pertuzumab (±chemotherapy), followed by monotherapy with trastuzumab (195 patients, 41%). Second line therapy was initiated by 206 patients (43%), with a median duration of 7 months, where trastuzumab emtansine was the most prevalent therapy, used by 84 patients (41%). Third line therapy was initiated in 119 patients (25%) and 55 patients (11%) proceeded to fourth line therapy. The 182 patients (28%) who did not receive any anti-HER2 therapy were older (74 years vs. 55 years) and had more comorbidity compared to treated patients. Among patients ≤75 years and healthy, 15% did not receive anti-HER2 therapy. Patient characteristics strongly influence anti-HER2 treatment patterns, and although numerous treatment options are available, a substantial proportion of HER2+ mBC patients did not receive targeted therapy. Undertreatment may be present.

Keywords: HER2+ metastatic breast cancer; population‐based cohort; real‐world data; vulnerable patient groups.

FIGURE 1

Proportion of patients receiving different anti‐HER2 therapies in Norwegian public hospitals from 2012 to 2022, according to the publication year of pivotal clinical study, and the year of international (FDA)‐ and national approval in Norway.

FIGURE 2

Sankey diagram of anti‐HER2 therapy user patterns for 2012–2022 (not including endocrine or chemotherapy) (n: 479), according to treatment line, , , with corresponding table showing number of patients starting each line of therapy (in total and according to specific therapy), median treatment duration in days (in total and according to specific therapy), and number of patients who are lost to follow‐up, censored due to cancer or die before the next line of therapy.

FIGURE 3

Overview of patients who received and who did not receive systemic cancer therapy (including chemo‐, endocrine‐ and anti‐HER2 therapy) among 661 patients registered with certain treatment information from 2012 to 2021, and corresponding patient characteristics.

FIGURE 4

Relative survival for all patients with HER2+ mBC according to age group at metastatic diagnosis and years since metastatic diagnosis.