BACKGROUND
Hypothyroidism (low thyroid hormone levels) is one of the most common endocrine diseases, affecting about 5% of general population. A previous study suggested that 15-20% of people who survived cancer in childhood may develop hypothyroidism later in life, which is much more common than in the general population. St. Jude Children’s Research Hospital has a large group of patients who are followed after their diagnosis and treatment of cancer in childhood. The researchers of this study assessed how often hypothyroidism occurred in these patients, what the risk factors of developing hypothyroidism were, and how the diagnosis of hypothyroidism affected these patients.

THE FULL ARTICLE TITLE
Chemaitilly W et al 2022 Primary hypothyroidism in childhood cancer survivors: Prevalence, risk factors, and long-term consequences. Cancer 128:606–614. PMID: 34643950.

SUMMARY OF THE STUDY
Patients who were at least 18 years old and had cancer in the last 10 years were included in the study. Patient who had serum thyrotropin (TSH) level above the upper limit of the normal range, indicating low thyroid hormone levels, or those who were taking thyroid hormone replacement, such as levothyroxine, were identified as having diagnosis of hypothyroidism. Whether a patient received radiation therapy to neck where thyroid gland is located was recorded. Later development of high blood pressure, diabetes, and high cholesterol levels, as well as physical and mental health, cognitive problems, and quality of life of these patients were assessed.

A total of 2965 patients, whose average age was 31 years old and had the initial cancer diagnosis 22.3 years ago on average, were included in the study.

Primary hypothyroidism was diagnosed in 14.7% (436 patients). Of those 436 patients with hypothyroidism, 31.9% (139 patients) had hypothyroidism after thyroidectomy to remove thyroid nodules, thyroid cancer, or enlarged thyroid gland (goiter). Radiation therapy to the area of thyroid gland as a part of the cancer treatment increased risk of developing hypothyroidism later. Patients with hypothyroidism were more likely to have high cholesterol levels and problems with physical health, such as having muscle weakness, low muscle mass, low energy level, or slow walking speed, or feeling less physically fit. Patients with free thyroxine (free T4) level on the lower end of normal range were more likely to have fat around abdomen and less likely to have problem with physical health and those with free T4 level on the higher end of normal range. Patients with low free T4 levels were more likely to have lower quality of life.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Hypothyroidism was diagnosed in almost 15% of patients who survived childhood cancer in this study. Hypothyroidism was about three times more common in these patients than in general population. Those with a diagnosis of hypothyroidism were also more likely to have high cholesterol levels and reported more problems with physical health.

Given the high prevalence and its potential association with other health problems, it would be important for treating clinicians of childhood cancer survivors, including primary care providers and oncologists, to watch out for development of thyroid dysfunction in these patients. It would be also important to educate childhood cancer survivors to be aware of potential symptoms of hypothyroidism to prompt screening if they develop symptoms consistent with hypothyroidism.

— Sun Y. Lee, MD MSc

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