Growth & height after childhood cancer treatment — what parents need to know

When a child is treated for cancer, the priority — rightly — is getting rid of the cancer. But some of the treatments that save a child's life can also affect how the body grows over the years that follow. This is known as a late effect: a consequence of treatment that appears months or years after treatment has ended.

Growth is controlled by a chain of signals. The hypothalamus in the brain signals the pituitary gland to release growth hormone (GH). GH then acts on the liver and growth plates in the bones to drive physical growth. Any treatment that disrupts this chain — particularly radiation to the brain — can slow or stop normal height gain.

Radiation is the most significant risk factor. Cranial radiation (radiation directed at the brain) can damage the hypothalamus and pituitary gland, reducing the amount of growth hormone the body produces. This is called growth hormone deficiency (GHD). The risk is higher when radiation doses are higher and when children are younger at the time of treatment. Radiation to the spine can also directly impair the growth of the vertebral bones — this is a separate mechanism from GHD and cannot be corrected by growth hormone injections alone.

Chemotherapy plays a smaller but real role. High-dose corticosteroids — given in leukaemia treatment — can suppress growth during the treatment period. Some chemotherapy medicines affect thyroid function, and an underactive thyroid (hypothyroidism) slows growth. Prolonged illness, reduced appetite, and lower physical activity during treatment also affect how well a child grows during those months.

The good news: many children catch up. Children treated without brain or spine radiation — for example, most leukaemia survivors and many solid tumour survivors treated with surgery and chemotherapy alone — often show catch-up growth after treatment ends and reach a normal adult height. The children at highest risk are those who received radiation to the brain or spine, particularly at a young age.

Ask at the one-year survivorship review. If your child received cranial or craniospinal radiation, bring up growth hormone at the twelve-month post-treatment follow-up — even if your child appears to be growing normally at that point. GHD often becomes apparent gradually. The growth velocity (how fast your child is growing, in centimetres per year) is more telling than a single height measurement. A printed growth chart with measurements going back to before treatment started is one of the most useful things you can bring to any survivorship appointment.

What the evaluation involves. The paediatric endocrinologist will review your child's growth chart, check an IGF-1 blood level, assess pubertal stage, and look at a bone age X-ray — a wrist X-ray that shows how many years of growth remain based on how mature the growth plates look. If IGF-1 is low or growth velocity is falling, a growth hormone stimulation test will be arranged. This test involves an overnight fast, a small intravenous line, and blood samples taken at intervals over two to three hours. It is an outpatient procedure, not a hospital admission.

Starting growth hormone replacement. If GHD is confirmed, daily injections of synthetic growth hormone are prescribed. The injections are small-volume subcutaneous (under the skin) injections that most families manage at home with training. They are usually given in the evening, at the same time each day. The dose is adjusted every three to four months based on growth response and IGF-1 levels. Treatment continues until the growth plates close — usually in the mid to late teens.

Is growth hormone replacement safe after cancer? This is the question most parents ask. Current international guidelines — from the Children's Oncology Group, the European Society for Paediatric Endocrinology, and the Endocrine Society — state that growth hormone replacement is considered safe in most childhood cancer survivors and does not appear to increase the risk of cancer relapse in most tumour types. The oncologist and endocrinologist will review your child's individual history together before making this decision. Some tumour types require a longer wait before starting GH — this is discussed case by case.

What about spinal radiation and sitting height? If your child received radiation to the spine, the shortening of the vertebral bones is a separate issue from GHD. Growth hormone treatment will not reverse this effect, because the bones themselves are shortened — not the hormone signal. This is important to discuss honestly with your family so expectations are realistic. However, GHD can occur alongside spinal radiation effects, and treating the GHD component is still worthwhile.