# Anti-HER2 treatment in everyday practice: how we treat older women with breast cancer differently

## TL;DR

Older women with HER2-positive breast cancer receive less anti-HER2 treatment in real-world practice, even after adjusting for health factors.

## Contribution

This study reveals a significant decline in anti-HER2 therapy use among patients over 75 in routine clinical practice.

## Key findings

- Anti-HER2 therapy use dropped from 83–95% in women under 75 to 8% in those aged 90 and older.
- Older patients had a reduced likelihood of receiving anti-HER2 therapy compared to younger patients, even after adjusting for comorbidities.
- Neoadjuvant anti-HER2 therapy also decreased with age, from 24% in younger patients to 12% in those over 75.

## Abstract

Targeted therapies have improved survival in human epidermal growth factor receptor 2 positive breast cancer (HER2 + BC). However, patients over 75 years of age are often excluded from clinical trials of anti-HER2 therapies, and it is unclear to what extent they receive these treatments in routine care. To address this, we examined age-related patterns of anti-HER2 therapy use in real-world clinical practice in Norway.

In a nationwide registry-based cohort, we identified women diagnosed with stage I-III HER2 + BC during 2012–2021. We investigated treatment patterns using descriptive statistics and estimated the direct effect of age on anti-HER2 therapy use by Poisson regression.

Among 3526 women with HER2 + BC, anti-HER2 therapy use was consistently high (83–95%) in those under 75 years, decreased to 60% at ages 75–79, and declined further with advancing age to 8% at ≥ 90 years. Neoadjuvant anti-HER2 therapy also decreased with age (from 24% in patients under 75 to 12% in patients over 75 years). Accounting for cancer characteristics, comorbidities, polypharmacy, and socio-economic factors, older patients had reduced likelihood of receiving any anti-HER2 therapy compared with patients younger than 55 (RR 0.75, 95% CI 0.66–0.85, p < 0.001, at age 75–84 and RR 0.21, 95% CI 0.11–0.41, p < 0.001, at age 85 +).

Anti-HER2 therapy use declined substantially after the age of 75 even when accounting for comorbidities and polypharmacy. Chronological age appears important in planning treatment for patients with HER2 + BC. Specific guidelines pertaining to older patients with HER2 + BC are needed to avoid potential undertreatment.

The online version contains supplementary material available at 10.1007/s10549-025-07888-z.