Childhood treatment with recombinant human growth hormone was associated with a significantly increased risk of cardiovascular events, based on data from more than 3,000 individuals.
“Both excess levels of growth hormone and [growth hormone deficiency] have been associated with increased cardiovascular morbidity and mortality,” but data on long-term cardiovascular morbidity in individuals treated with growth hormone in childhood are lacking, wrote Anders Tinblad, MD, of Karolinska Institutet, Stockholm, and colleagues.
In a population-based cohort study published in, the researchers identified 3,408 Swedish patients treated as children with recombinant human growth hormone (rhGH) between Jan. 1, 1985, and Dec. 31, 2010, and compared each with 15 matched controls (a total of 50,036 controls). The patients were treated for one of three conditions: isolated growth hormone deficiency (GHD), small for gestational age (SGA), and idiopathic short stature (ISS).
Data on cardiovascular outcomes were collected from health care and population-based registers and analyzed between Jan. 1, 1985, and Dec. 31, 2014. The average age of the participants at the study’s end was 25.1 years.
In all, 1,809 cardiovascular disease events were recorded over a median follow-up period of 14.9 years, for an incidence rate of 25.6 events per 10,000 person-years in patients and 22.6 events per 10,000 person-years in controls.
When separated by sex, the incidence was higher in female patients compared with controls (31.2 vs. 23.4 events per 10,000 person-years, respectively, but similar in male patients vs. controls (23.3 vs. 22.3 events per 10,000 person-years). “Differences in estrogen levels or responsiveness to rhGH treatment have previously been hypothesized as possible explanations, but the underlying mechanism for this sex difference still remains unclear and merits further investigation,” the researchers wrote.
Overall, the highest adjusted hazard ratios occurred in subgroups of patients with the longest treatment duration (HR 2.08) and highest cumulative dose of growth hormone (HR 2.05), but no association was noted between highest daily hormone dose and cardiovascular event risk. Hazard ratios were higher across all three treatment subgroups of SGA, GHD, and ISS compared with controls (HR 1.97, 1.66, and 1.55, respectively).
“The association between childhood rhGH treatment and CVD events was also seen when assessing only severe CVD outcomes, but with even lower absolute risks,” the researchers noted.
The study findings were limited by several factors including the potential for confounding by treatment indication and the lack of long-term follow-up data given the relatively young age of the study population, the researchers said. The results were strengthened by the large sample size and showed that the absolute risk for overall and severe cardiovascular disease in children treated with growth hormones was low, “which could be reassuring to individual patients,” they added. However, “At the group level, and perhaps especially for female patients and those treated for SGA indication, further close monitoring and future studies of CVD safety are warranted,” they concluded.
Safety and ethical concerns persist
Although the study authors cite limited conclusions on causality and low absolute risk, several issues persist that prompt ongoing analysis of pediatric growth hormone use, namely “worrisome indirect evidence, challenges and limitations in the direct evidence, and the changing world of growth hormone treatment,” Adda Grimberg, MD, of the University of Pennsylvania, Philadelphia, wrote in an.
“Although evidence asserts that neither growth hormone nor insulinlike growth factor I is carcinogenic, the basic science and oncology literatures are rife with reports showing that they can make aberrant cells more aggressive,” and such indirect evidence supports the need for more direct evidence of possible harm from growth hormone treatment, Dr. Grimberg wrote. Most current safety data on growth hormone come from postmarketing surveillance studies, but these studies do not include controls or data on outcomes after discontinuation of treatment, she noted.
The current study, while able to follow patients across the lifespan, cannot indicate “whether the small but increased risk of cardiovascular disease found in this study was caused by the pediatric growth hormone treatment that identified the participants, by the conditions being treated, by other potential confounder(s) not captured by the study’s methods, or by a combination of the above,” said Dr. Grimberg.
In addition, “the move from replacement of GHD to pharmacologic height augmentation in children who already make sufficient growth hormone had the potential to change the safety profile of treatment,” she said.
“Parents of patients in pediatric primary care practices and of patients seeking growth-related care in a subspecialty endocrine clinic rated treatment characteristics (i.e., proven efficacy and safety) as the factor most having a big or extreme effect on their growth-related medical decision-making,” Dr. Grimberg said. “The centrality of treatment safety to patient-family decision-making underscores the importance of continued scrutiny of growth hormone safety as the treatment and its recipients continue to evolve,” she concluded.
The study was supported by the Swedish Research Council, the Stockholm City Council, the Karolinska Institute, the Society for Child Care, Sahlgrenska University Hospital, and the Stockholm County Council’s combined clinical residency and PhD training program. Lead author Dr. Tidblad disclosed funding from the Society for Child Care and Stockholm County Council during the conduct of the study and personal fees from Pfizer. Dr. Grimberg disclosed serving as a member of the steering committee for the Pfizer International Growth Study Database, and as a consultant for the Pediatric Endocrine Society GH Deficiency Knowledge Center, sponsored by Sandoz AG.