Thyroid function after cancer treatment
How chemotherapy and radiotherapy impact thyroid function
An unfortunate side effect of cancer treatment is developing thyroid problems—this can occur from both radiotherapy and chemotherapy. While most thyroid problems happen within five years of completing cancer treatment, for some people thyroid problems might happen decades after treatment (1).
Underactive thyroid caused by radiotherapy
Radiotherapy aimed at the head and neck might affect the thyroid gland, causing it to become underactive.. Radiotherapy has a huge impact on thyroid cells, causing many to die, as well as changing the inner structure of the thyroid gland and causing chronic inflammation (2).
This effect of radiotherapy typically occurs years after treatment, , on average about 2–7 years later depending on the dose and the length of the treatment (3-5).
Half of patients who receive radiotherapy will develop an underactive thyroid (6-9).
Underactive thyroid caused by chemotherapy
Both traditional chemotherapy as well as its “smart” drugs (medications that target specific molecules almost exclusively found in cancer cells) can also cause hypothyroidism. Chemotherapy can cause an underactive thyroid in 7 in 10 patients (10-13).
Smart drugs that may cause side effects include (14 - 23):
Traditional chemotherapy (through medications such as Cytoxan, Neosar, Methotrexate, Adrucil, Carac, Efudex, Efudix, Navelbine, Adriamycin, Caelyx, Myocet, Blenoxane, Velban, DTIC-Dome, Prednisolone, Matulane, Natulan, Indicarb, Oncovin, Vincasar, Platinol, Etopophos, Toposar, Ellence, Xeloda, Eloxatin, Leucovorin, Nolvadex, Genox, Tamifen) can also affect thyroid function (24).
Furthermore, drugs modulating the immune system (including interleukin-2, interferon-alpha, Thalomid, and Revlimid) can also cause an underactive thyroid (25-27). If an underactive thyroid occurs when a patient is treated with this type of medication, it usually happens around 4 months after starting treatment (28).
The drug ipilimumab (Yervoy) affects thyroid indirectly, by triggering autoimmune destruction of the pituitary gland which leads to lower TSH and an underactive thyroid (28).
How to get diagnosed post-treatment
Thyroid problems can happen at any point—between a few weeks to several decades after the cancer treatment. It depends on the type of therapy, dosage, and duration of treatment, as well as individual genetic predispositions.
The most common signs and symptoms of an underactive thyroid are fatigue, weight gain, sleep problems, and headaches. However, lots of people experience less common symptoms as well.
If you suspect you might have an underactive thyroid, tell your doctor the details of your cancer treatment, as well as the intensity and the type of symptoms you are currently experiencing.
This will help your doctor with establishing your health history and with selecting an appropriate way to manage your condition.
Download BOOST Thyroid today. You can track your symptoms and quickly gauge if and how well your treatment is working.
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