For individuals who have undergone treatment for thyroid cancer, the prospect of a new, unrelated cancer diagnosis can be a concern. A secondary cancer is a completely new primary cancer that develops in a different part of the body. It is not a recurrence or spread of the original thyroid tumor.
The development of a secondary cancer is a separate medical event, with its own diagnosis and treatment. Studies have shown that thyroid cancer survivors have a higher likelihood of developing a second primary cancer compared to the general population.
This elevated risk is associated with several factors, including the treatments used for the initial thyroid cancer. Awareness of this possibility allows for proactive health management and informed discussions with healthcare providers.
Differentiating Secondary Cancer from Recurrence
Understanding the terminology used by medical professionals is helpful. When discussing cancer, three terms can be confused: secondary cancer, recurrence, and metastasis. A secondary cancer, as previously mentioned, is an entirely new cancer. For example, a person successfully treated for thyroid cancer could later develop breast cancer; this would be a secondary primary cancer.
In contrast, a recurrence means the original thyroid cancer has returned after a period of being undetectable. This can happen in the same location as the original tumor or in the lymph nodes in the neck, and the cells are thyroid cancer cells.
Metastasis is the process where the original cancer cells spread to distant parts of the body. For instance, thyroid cancer cells might travel and form new tumors in the lungs or bones, but these new tumors are still considered thyroid cancer.
Risk Factors from Thyroid Cancer Treatment
The treatments effective against thyroid cancer can also be a source of risk for developing a secondary cancer. Radioactive Iodine (RAI) therapy is a common treatment for differentiated thyroid cancer, particularly after surgery. RAI works by targeting and destroying any remaining thyroid cells, but other tissues can absorb small amounts of radiation, which may lead to cellular damage and a new cancer.
The risk associated with RAI is related to the cumulative dose received; higher doses are linked to a greater chance of developing a second cancer. Studies show that RAI treatment is associated with an increased risk for both leukemia, which tends to appear within a few years, and solid tumors, which may not become apparent for a decade or more.
External Beam Radiation Therapy (EBRT) is another treatment that uses radiation, although it is used less frequently for thyroid cancer. Like RAI, EBRT can affect healthy tissues surrounding the targeted area, which can increase the long-term risk of a new cancer in that region.
The decision to use these treatments is based on weighing the benefits of treating the thyroid cancer against the potential long-term risks. The absolute increase in risk is considered small for most individuals, and the benefits of treatment far outweigh the long-term risk of a secondary malignancy.
Common Secondary Cancers
Research has identified several types of secondary cancers that are more commonly observed in thyroid cancer survivors, particularly those treated with radioactive iodine. Leukemia, specifically acute myeloid leukemia (AML), is one of the most frequently cited. The risk for leukemia is thought to be due to the effect of radiation on the bone marrow, where blood cells are produced.
Cancers of the salivary glands are also seen with increased frequency because the salivary glands, like the thyroid, absorb iodine. When a patient receives RAI, the salivary glands can be exposed to radiation, which can lead to cancer in these tissues over time. Other solid tumors have also been linked to prior thyroid cancer treatment, including:
- Breast cancer
- Uterine cancer
- Lung cancer
- Colorectal cancer
The overall risk of developing any of these secondary cancers remains relatively low for any given individual. Awareness of these specific cancer types can help guide long-term screening and monitoring for thyroid cancer survivors.
Long-Term Monitoring and Health Management
A survivorship care plan, developed with your oncology team, is a useful tool for managing long-term health. This document summarizes your diagnosis, treatments received, and recommendations for follow-up care.
Keeping a detailed record of your treatment, including specific doses of radioactive iodine, is important for future medical consultations. Regular follow-ups with providers knowledgeable about your history allow for monitoring of thyroid cancer recurrence and discussion of new health concerns.
These appointments also ensure you are current on all standard, age- and gender-appropriate cancer screenings. Living a healthy lifestyle can contribute to well-being and may help lower the risk of a new cancer.
This includes maintaining a healthy weight, eating a balanced diet, regular physical activity, and avoiding tobacco. It is also important to be aware of your body and to report any new or persistent symptoms to your doctor without delay.