All Thiopurines Are Equal But Some Thiopurines Are More Equal—Reply

In Reply Meijer and de Boer offer a valid examination of our study conclusions for azathioprine sodium association with therapy-related myeloid neoplasm that excludes mention of 6-mercaptopurine. As highlighted in our article's Limitations section, small sample size, particularly for individual drug classification, limits interpretation, because many of these comparisons are underpowered, resulting in nonsignificant odds ratios and associated wide confidence intervals. Notably, only 12 patients received mercaptopurine in our study of 86 patients (3 cases and 9 controls), resulting odds ratio, 0.62 (95% CI, 0.15-2.53), thus statistically nonsignificant at P = .51. Indeed, a multivariate model was constructed in which agents with P < .20 were included and only azathioprine remained significant (odds ratio, 6.92; 95% CI, 2.21-21.66) when controlling for cyclophosphamide, methotrexate sodium, and leflunomide use. To elucidate further questions on nonsignificant results from our study requires a larger sample size or prospective investigations.

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