To the Editor We read with interest the observational cohort study by Margolis and colleagues1 that evaluated the risk of cancer among patients in the Pediatric Eczema Elective Registry who were exposed to pimecrolimus. The authors reported that the overall incidence rates of all cancers were not significantly higher than expected rates based on age-standardized rates from the Surveillance, Epidemiology, and End Results database. While it is certainly heartening to note these reassuring results, we are concerned about the age-specified incidence rate of leukemias among the age group 0 to 4 years in this study. There were 2 cases of acute lymphoblastic leukemia (ALL) in 2 African American children aged 0 to 4 years. Given a follow-up duration of 2585.10 person-years, the rate of leukemia would be 77.4 per 100 000 person-years (calculated as 2 cases per 2585.10, times 100 000). This is significantly higher than the expected rates of leukemia (7.9 per 100 000 person years). Notably, ALL is the most common pediatric cancer, with a peak incidence at age 2 to 5 years; therefore, evaluating the subgroup incidence rate ratio among children aged 0 to 4 years would be relevant.
Yew YW, Tey HL. Association Between Leukemia and Topical Use of Pimecrolimus. JAMA Dermatol. 2015;151(12):1390-1391. doi:10.1001/jamadermatol.2015.3445