Herpes zoster risk among female survivors of breast cancer in Japan.
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BACKGROUND: Survivors of breast cancer (BC) have a higher risk of developing herpes zoster (HZ), but it remains unclear how this risk is affected by time since BC diagnosis and treatment regimen. METHODS: This matched cohort study used a large health-insurance claims database including Japanese employees and their families. Between January 2005 and December 2019, women aged 18-74 years with and without incident BC were matched 1:4 by age and timing of database entry, in the month of BC diagnosis. This study aimed to evaluate the risk of developing HZ in female BC survivors compared with women without BC, to examine temporal variations in risk during survivorship, and to assess the impact of different BC treatments on this risk. We compared the first HZ incidence using stratified Cox regression analyses over the study period, divided by follow-up length. We then estimated HZ risk by treatment regimen using unstratified Cox regression analysis, with follow-up beginning 1 year after matching. RESULTS: Comparing 23,169 BC survivors vs 92,801 matched women without BC (median age: 49.4 years, interquartile range: 44.7-56.0 years), the HZ incidence rate (95% confidence interval) was higher in the survivors (16.5 [15.6-17.5] vs 10.6 [10.3-11.0]/1000 person-years), with an adjusted hazard ratio (aHR) of 1.57 (1.46-1.68) over the whole period. This aHR decreased over time but remained elevated up to 10 years (0-1 year: 1.90 [1.68-2.16]; 1-2 years: 1.64 [1.42-1.89]; 2-3 years: 1.30 [1.08-1.57]; 3-10 years: 1.37 [1.20-1.56]). The aHRs were 1.15 (0.98-1.36), 1.64 (1.16-2.30), 1.23 (0.94-1.62), and 1.60 (1.30-1.97), respectively, for survivors who received no chemotherapy, anthracycline-only, taxane-only, and anthracycline-plus-taxane, compared with women without BC. CONCLUSIONS: Female BC survivors in Japan had a higher HZ risk compared with the general age-matched female Japanese population. HZ vaccination should therefore be promoted for BC survivors.