No Significant Association Between Herpes Zoster and Breast Cancer: A German Outpatient Study with over 120,000 Participants

Purpose: The purpose of this study was to investigate a possible association between Herpes Zoster (HZ) and the subsequent diagnosis of breast cancer (BC). Methods: Utilizing the Disease Analyzer database, anonymized medical records from German office-based practices were accessed. Longitudinal data of female patients aged 18 years and above diagnosed with HZ between 2005 and 2021 were included. Individuals without HZ diagnoses were matched to HZ patients using a nearest neighbor propensity score matching (1:1) based on age, sex, index year, average yearly consultation frequency during the follow-up, and predefined co-diagnoses. The incidence of BC in the cohort with and without HZ was evaluated using Kaplan–Meier curves and compared using the log-rank test. Finally, a univariable Cox regression analysis was conducted to assess the association between HZ and BC. Results: This study included 64,255 women with HZ and an equal number without HZ, with comparable characteristics in terms of age, visit frequency, and comorbidities. Analysis revealed no significant association between HZ and subsequent BC incidence, with similar rates observed in both HZ and non-HZ cohorts across different age groups. Conclusions: In this retrospective cohort study consisting of well-matched patients, the results indicate no significant association between an HZ infection and the development of BC over a 10-year follow-up period. This is the largest study of its kind to date.