Better treatment for childhood cancer has lead to improved survival rates.1,2 However, this success has been accompanied by an increased risk of late complications and early mortality.3
Prevalent late effects seen in childhood cancer survivors include endocrine system disorders, which make up about 5% of all late complications.4
The thyroid gland is found in the neck and controls the body's metabolic rate (how quickly energy is used up by the body).
The thyroid produces two main hormones which regulate the rate of metabolism:
The gland is controlled by TSH = Thyroid stimulating hormone
TSH is produced by the pituitary
Cancer survivors are most at risk for hypothyroidism (under-activity of the thyroid gland) as a complication of their previous treatment. The thyroid is small and atrophied and does not produce enough T3 or T4. This is called "primary" hypothyroidism. Radiation therapy (RT) to the thyroid or tissues immediately adjacent to the thyroid is the commonest cause of thyroid problems.
Sometimes the problem can be that the pituitary is damaged and is unable to produce enough TSH (this is called "central" hypothyroidism).
There are 2 parts to the pituitary:
1. Anterior pituitary: produces many important hormones
- Growth hormone (GH)
- Thyroid Stimulating Hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Prolactin (PRL)
- Luteinizing hormone (LH)
- Follicle stimulating hormone (FSH)
- melanocyte–stimulating hormones (MSH's)
These hormones are released from the anterior pituitary under the influence of the hypothalamus.
2. Posterior pituitary: stores and releases the following hormones
Cranial RT is the commonest cause of pituitary dysfunction. Often these patients have "panhypopituitarism" which means that there are very reduced levels of all the pituitary hormones (though GH deficiency is commonest).
Some diseases directly damage the pituitary and patients present with pituitary hormone deficiencies before they have had any treatment - such as craniopharyngioma and Langerhans cell histiocytosis (LCH).