A team of international researchers has discovered that patients who survive thyroid cancer have a 30% increased risk of developing a second primary cancer, and conversely, those who have had a primary cancer in other organs are at increased risk of subsequent thyroid cancer.
They highlight that clinicians should be aware of the increased risk of developing secondary cancers when treating patients with primary thyroid cancer.
"People who have had thyroid cancer have increased risk of cancer in other organs."
The team explains in the Journal of Clinical Endocrinology & Metabolism that survival rates following thyroid cancer have increased steadily in recent years, possibly because of improved clinical practice and diagnosis.
This has led to claims that the incidence of secondary cancers following thyroid cancer survival may be increasingly likely, particularly following the use of radioiodine treatment.
To test this idea, they combined data from 13 population-based cancer registries from Europe, Canada, Australia, and Singapore. The patient cohort comprised 39,002 individuals with thyroid cancer, among whom 74% were female and 57% were younger than 56 years.
During a follow-up period of 25 years in which patients were monitored for secondary thyroid cancers, 2821 other cancers were diagnosed; giving a risk of second primary cancer after first primary thyroid cancer of 1.31 compared with the general population.
For the total period of follow up, significantly elevated risks were seen for many cancers, including those of the salivary gland, small intestine, prostate, breast, and adrenal gland, as well as leukemia. Most of these cancers were detected within the first year following thyroid cancer diagnosis.
Importantly, the investigators also found that 1990 patients developed thyroid cancer after being diagnosed with another cancer. There were significantly elevated risks of secondary primary thyroid cancer after cancers of the esophagus, breast, stomach, colon, pancreas, and bone.
Speaking with Medwire News, lead author Mark Strachan, from the Western General Hospital in Edinburgh, UK, summarized: "People who have had thyroid cancer have increased risk of cancer in other organs."
Moreover, he explained that scientists have long been suspicious that radioiodine treatment for thyroid cancer may raise the risk of breast cancer as the breast readily takes up the substance.
However, he contended that the bidirectional links identified in the present study "indicate that radioiodine treatment is unlikely to explain all of the increased cancer risk after initial thyroid cancer, and genetic and environmental factors more probably explain the association."