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To the Editor: Dr Steinberg and colleagues¹ reported a 40% reduction in mortality among patients with SCA who used hydroxyurea (P = .04), without statistically significant toxicity. The authors pointed out that theirs was an observational study of self-selected treatment. Despite the authors' caution, we are concerned that they are overly optimistic in their conclusions.

The authors pointed out the possibility of survival selection bias, but did not address this in their analysis. Specifically, no attempt was made to address the potential differences in demographics (eg, age, sex, baseline severity of disease) between the treatment groups after self-selection. Comparing the 2 groups based on cumulative exposure to hydroxyurea exaggerates survival bias, minimizes the effect of discontinuation of therapy because of toxicity, and ignores the possibility that the sickest patients may be the first to withdraw from treatment. Such an analysis could find a statistical difference even if the therapy . . . [Full Text of this Article]

Dean Anthony Lee, MD, PhD; Brigitta U. Mueller, MD
Department of Pediatrics
Baylor College of Medicine
Houston, Tex

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