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Immortal person-time bias in the association between herpes zoster and survival following autologous stem cell transplantation

Bone Marrow Transplantation volume 50, pages 878–879 (2015)Cite this article

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In a recent study Kamber et al.1 evaluated the prognostic significance of herpes zoster (HZ) in 191 consecutive myeloma patients treated with high-dose melphalan chemotherapy followed by autologous stem cell transplantation (ASCT). The study provides interesting and important data on the burden of HZ in this patient population. However, immortal person-time bias likely affected the methods used to estimate the effect of HZ on survival after ASCT, leading to the spurious appearance of a protective effect.

Kamber et al.1 reported a 66% reduction in mortality among patients with HZ after ACST compared with patients without HZ after ASCT, which suggests that HZ infection after ASCT is more beneficial than most tumor-directed therapies. In the discussion, the authors expressed their surprise about the results, but nevertheless put forth some potential biological explanations. Because HZ can take a complicated course in patients with haematological malignancies2 and may correlate with degree of immunosuppression,3, 4 their results seem biologically implausible. More likely, the decreased mortality in patients with HZ results from immortal person-time bias.

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References

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Authors and Affiliations

  1. Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark

    S A J Schmidt & T L Lash

  2. Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA, USA

    T L Lash

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  1. S A J Schmidt
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  2. T L Lash
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Correspondence to S A J Schmidt.

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Schmidt, S., Lash, T. Immortal person-time bias in the association between herpes zoster and survival following autologous stem cell transplantation. Bone Marrow Transplant 50, 878–879 (2015). https://doi.org/10.1038/bmt.2015.66

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