A nationwide cohort study found an association between a woman’s use of hormonal contraceptives and a small increased risk of nonlymphoid leukemia in her offspring.
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Maternal use of hormonal contraception either during pregnancy or in the 3 months beforehand was associated with a 46% higher risk of any leukemia in the children (P = .011), compared with no use, Marie Hargreave, PhD, of the Danish Cancer Society Research Center and her coauthors reported in Lancet Oncology.
The study of 1,185,157 children born between 1996 and 2014 included data from the Danish Cancer Registry and Danish National Prescription Registry and followed children for a median of 9.3 years.
Use during pregnancy was associated with a 78% higher risk of any leukemia in the offspring (P = .070), and contraception use that stopped more than 3 months before pregnancy was associated with a 25% higher risk of any leukemia (P = .039).
The researchers estimated that maternal use of hormonal contraceptives up to and including during pregnancy would have resulted in about one additional case of leukemia per 47,170 children; in other words, 25 additional cases of leukemia in Denmark from contraceptive use from 1996 to 2014.
The increased risk appeared to be limited to nonlymphoid leukemia only. The risk with recent use was more than twofold higher (HR, 2.17), compared with nonuse, and use during pregnancy was associated with a nearly fourfold increase in the risk of leukemia (HR, 3.87).
“Sex hormones are considered to be potent carcinogens, and the causal association between in-utero exposure to the oestrogen analogue diethylstilbestrol and subsequent risk for adenocarcinoma of the vagina is firmly established,” Dr. Hargreave and her colleagues wrote. “The mechanism by which maternal use of hormones increases cancer risk in children is, however, still not clear.”
Recent use of combined oral contraceptive products was associated with a more than twofold increased risk of nonlymphoid leukemia in offspring, compared with no use. However progestin-only oral contraceptives and emergency contraception did not appear to increase in the risk of lymphoid or nonlymphoid leukemia.
The association was strongest in children aged 6-10 years, which the authors suggested was likely because the incidence of nonlymphoid leukemia increases after the age of 6 years.
While acknowledging that the small increase in leukemia risk was not a major safety concern for hormonal contraceptives, the authors commented that the results suggested the intrauterine hormonal environment could be a direction for research into the causes of leukemia.
The study was supported by the Danish Cancer Research Foundation and other foundations. One author reported grants from the sponsoring foundations and another author reported speaking fees from Jazz Pharmaceuticals and Shire Pharmaceuticals.
SOURCE: Hargreave M et al. Lancet Oncol. 2018 Sep 6. doi: 10.1016/S1470-2045(18)30479-0.