Increased risk of varicella-zoster virus infection in patients with breast cancer after adjuvant radiotherapy: A population-based cohort study

Background/Purpose Limited evidence has been obtained on varicella-zoster virus (VZV) infection in patients with breast cancer as a complication related to adjuvant radiotherapy. We conducted a cohort study aimed to assess the risk of VZV infection in this patient setting. Materials and methods We used the National Health Insurance Research Database to identify 65,981 patients with breast cancer in Taiwan who underwent breast surgery between 2000 and 2011. After a 1:1 propensity score match was obtained between patients with and without radiotherapy, a competing risk regression model was constructed to estimate the hazard ratios and the incidence rate difference (IRD) of VZV infection in the patients with breast cancer receiving radiotherapy and those not receiving radiotherapy. Results After adjusting for covariates, the radiotherapy cohort showed a 1.51-fold higher risk (95% confidence interval = 1.06-5.16, p = 0.02, IRD = 4.98/10000 person-years) of subsequent VZV infection than the nonradiotherapy cohort. Furthermore, VZV infection risk was 3.85-fold higher among patients aged > 65 years who received radiotherapy than among those of the same age who did not receive radiotherapy (95% confidence interval = 1.1-13.4, p < 0.05, IRD = 11.09/10000 person-years). The risk increased with adjusted hazard ratio of 6.6 (95% confidence interval I = 1.51-28.8, p < 0.05, IRD = 32.01/10,000 person-years) and 7.08 (95% confidence interval = 1.64-30.5, p < 0.01, IRD = 35.72/10,000 person-years) in follow-up period less than 3 months and 3-5 months respectively. Conclusion Radiotherapy was associated with an increased risk of VZV infection among patients with breast cancer. The risk was significantly higher in older patient (>65 years old) and/or those who received chemotherapy. Regular clinical follow-up and additional serological testing in the first 5 months after radiotherapy are recommended.