A new study published in the Journal of Vascular Anomalies provides reassuring news for families whose children are taking sirolimus, a medication commonly used to treat complex vascular anomalies, including some lymphatic malformations.
What Are Vascular Anomalies?
Vascular anomalies are conditions caused by abnormal development of blood vessels, lymphatic vessels, or both. Depending on their size and location, they can cause pain, swelling, bleeding, infections, difficulty with movement, and other serious complications.
Many vascular anomalies are driven by genetic changes that affect pathways controlling cell growth. Sirolimus works by slowing one of these pathways, called mTOR, helping to reduce abnormal vessel growth and improve symptoms.
While sirolimus has been used successfully for more than a decade, families and physicians have continued to wonder whether a medication that slows cell growth could also interfere with a child's normal height and weight gain.
How Was the Study Conducted?
Researchers at Texas Children's Hospital's Vascular Anomalies Center reviewed the medical records of patients treated with sirolimus between 2008 and 2023. Initially, 232 patients had received the medication, but only children who had taken sirolimus consistently for at least two years were included in the final analysis. After applying those criteria, the study examined 50 children and adolescents.
The group included:
- 26 boys
- 24 girls
- Children ranging from birth to 18 years of age when treatment began
Researchers collected height and weight measurements at several time points:
- Before starting sirolimus
- 3 months after starting treatment
- 6 months after starting treatment
- 2 years after starting treatment
Instead of simply comparing children to one another, researchers compared each child to their own growth trajectory using standardized CDC growth charts. This approach allowed them to determine whether children stayed on their expected growth curve over time.
What Did the Researchers Find?
The study found that children maintained their expected growth patterns while receiving sirolimus.
When researchers analyzed changes in height and weight percentiles over the two-year period, they found no statistically significant differences in either boys or girls. In other words, children generally continued growing as expected for their age and sex.
The researchers also looked separately at a small group of children with Kaposiform Hemangioendothelioma (KHE) and Tufted Angioma, conditions that often require slightly higher sirolimus levels. Even in this group, no concerning growth trends were identified.
What About Babies Treated Very Early?
The study involved infants who started sirolimus before or shortly after birth because of severe vascular anomalies.
The authors highlighted examples of children who received sirolimus prenatally and continued treatment through infancy. Despite the understandable concerns about growth during these critical early years, their growth charts showed continued progress without evidence of growth suppression.
While these examples represent only a few patients, they provide additional information for families facing difficult treatment decisions in infancy.
Why Does This Matter?
For many families, concerns about growth can influence treatment decisions. This study is important because it focuses on children with vascular anomalies rather than transplant patients or other populations that may have additional health conditions affecting growth.
The findings suggest that long-term sirolimus treatment does not appear to slow normal height or weight gain in children with vascular anomalies, at least over a two-year period.
What Are the Limitations?
- Like all research, this study has limitations.
- It was conducted at a single center.
- Only 50 patients met the criteria for analysis.
- The study looked at growth over two years, so questions remain about treatment lasting much longer.
- Researchers reviewed existing medical records rather than conducting a prospective clinical trial.
The authors note that larger studies will be needed to better understand growth outcomes in children who remain on sirolimus for many years.
What Does This Mean for Families?
If your child is taking sirolimus—or your care team is recommending it—this study states that the medication does not appear to negatively affect normal growth in height or weight during the first two years of treatment.
That does not mean every child will have the same experience. Ongoing monitoring remains important, and treatment decisions should always be made with your vascular anomalies team. But these findings provide valuable information for families weighing the benefits and risks of long-term therapy.
At the Lymphatic Malformations Alliance, we know that families are not only managing a medical condition—they are navigating uncertainty, difficult decisions, and unanswered questions. Research like this helps bring greater clarity to those decisions and provides evidence that can support more informed conversations with healthcare providers.
Progress happens one study at a time. And every new answer helps families move forward with greater confidence and hope.
