Ask Thry'vors Archive Categories

• Beginnings
• Pathology and Cytology
• Surgery
• Treatment and Follow-up
• Radioactive Iodine
• Low Iodine Diet
• Thyroid Hormone Replacement and TSH Level
• Psychological impact of Thyroid Cancer
• Other Related Health Issues
• Women's Issues
• Men's Issues
• Children and Youth Issues

Women's Issues

1. Does thyroid cancer and/or treatment with RAI increase ones chances of getting breast cancer?

   Rosen (Nov 1/05)

   About a decade ago papers were presented that tried to associate breast and thyroid cancer. It did not take long before the counter argument was made that these were both diseases that particularly affected women and no strong cause and effect existed. This certainly represents my attitude and I am not aware of any different feeling amongst the endocrine surgeons that I associate with. This would not apply to individuals who have had undue exposure to external radiation which is carcinogenic for both organs.

   Radioactive Iodine therapy is not thought to induce breast cancer. There is a great deal on the web about breast cancer and the notion of surveillance in well patients. Personally I recommend annual mammography plus breast ultrasound after age 45, earlier if the patient has a strong family history of breast cancer or breast problems as well as a physician exam on at least an annual basis.

   Individualization of management is still important. Patients who have a family history of breast ca should undergo genetic counselling and testing where indicated for enhanced detection of breast cancer.

   True prevention is still a debatable topic. There is no set program although both surgical and medical means are being used in high risk women i.e. those with strong family history of breast ca.

    

   Ezzat (Nov 1/05)

   There are very rare families where thyroid cancer has been found in the same patients with breast cancer. In the vast majority of patients, however, these two common types of cancer appear to be independent.

   There is no evidence linking breast cancer with radioactive iodine use. In the absence of a special family history, there are no unique or special measures required for the prevention and monitoring of breast cancer in patients with known thyroid disease.

2. Some patients enter menopause earlier than expected due to thyroid cancer and/or treatment with RAI. Can menopause play a part in "brain fog"? What other factors may be playing a part in this phenomenon? Is there any literature regarding this phenomena?

   Cheng (March 1/09)

   The relationship between menopause and thyroid hormone is that thyroid hormone requirements change when one reaches menopause. One of the reasons for this is that estrogenstatus is related to the amount of thyroid hormone binding globulin which affects the amount of free thyroid hormone. In addition, other changes related to menopause (e.g. weight gain) will also affect thyroid hormone requirements.
   
   Bernstein (March 1/09)

   There is a fair bit of literature on the relationship between estrogen and cognitive functions, including in the 'normal aging' literature - looking at women before and after menopause, and also in young women over the course of their cycle (when estrogen levels fluctuated). In general, some cognitive abilities are worse when estrogen levels are lower, including verbal abilities and verbal memory (and some others might be better- like mental rotation). It's not that a person's abilities bottom out to an 'impaired' range, just that they aren't quite as good as expected, or as good as the person herself feels she used to be.
   
   As far as relieving the symptoms of poor concentration, increased distractibility, etc., I can only comment on behavioural changes that can help reduce the impact of them. Regardless of the reason for a person's 'brain fog' (assuming it's mild, and not a progressive dementia) -- say, for example, 'chemo-fog', mild depression, anxiety -- similar strategies can be effective to reduce the number of 'mistakes' made, such as using calendar, to-do lists, staying organized, etc.
   
   
    

3. How long should one wait to conceive, following treatment with RAI?

   Ain (April 1/07)

   There is no established reason to wait "6 months" from radioactive iodine therapy before conceiving a child. There is no appreciable radiation dose to the embryo if it forms more than 6 WEEKS from therapy. In addition, the only documented risk to the fetus comes from hypothyroidism in the mother causing reduced IQ after birth. If levothyroxine therapy was started after the radioiodine therapy, then the mother should not be hypothyroid by 6 WEEKS after the therapy. Taken in its entirety, I know of no reason to suspect any adverse effect whatsoever from radioiodine therapy on a woman's offspring, provided that conception took place at least 6 WEEKS after the therapy. I would certainly not base such an important decision upon the faulty warnings of an uninformed physician.

    

   Driedger (April 1/07, revised Sept 26/08)

   If kidney function is normal, radioiodine is about 95% eliminated from the body within about 3 days and the remainder within a couple of weeks. The germ cells from which the baby is conceived have a unique repair capacity, known as recombinant repair that corrects persisting DNA damage before the cell undergoes the final division prior to becoming an egg cell. Those eggs that have persistent damage are most likely to die and are certainly less competitive for fertilization.

   In the past, most physicians recommended that patients not embark on a pregnancy for a year after a radioiodine therapy, not because of radiation issues, but because there seemed to be a higher incidence of spontaneous abortions in those who become pregnant sooner. A follow-up report (2008) from the same clinic has withdrawn this earlier recommendation. The probability of a thyroid or other abnormality in the baby is not increased so far as we can tell; The BEIR VII (Biological Effects of Ionizing Radiation) Committee states that is there is any effect at all, it would require a study of 30,000 patients to measure it.

4. What should I be aware of in regards to becoming or being pregnant with thyroid cancer?

   Feig (June 1/06)

   Aside from the occasional report suggesting pregnancy may lead to an increased growth of thyroid cancer because of the elevated HCG (human chorionic gonadotropin) which acts like TSH to increase thyroid production, most studies suggest that pregnancy does not affect the course of thyroid cancer.

   If a woman is discovered to have well-differentiated thyroid cancer during the first trimester, she may elect to have the surgery done during the second trimester. The risk of miscarriage during the second trimester from surgery is quite low. However, if she chooses not to have surgery during the second trimester, or is discovered to have thyroid cancer during the third trimester, there is no evidence (except for one case described) that the delay results in a worse outcome.

   (If a woman is on thyroid hormone replacement, the levels need to be followed during pregnancy) because there is an increased demand for thyroid hormone. This is because of an increase in thyroid binding globulin which binds free thyroid hormone, and because of increased clearance of iodine. For these reasons, the dose of thyroid hormone needs to be increased, or the woman may potentially become hypothyroid.  The fetus is not fully able to make thyroid hormone until 18-20 weeks gestation, so it is dependent on the mother for thyroid hormone during this time. Some investigators have hypothesized that low levels in the first trimester may translate into developmental problems in the baby. Hypothyroidism, or low levels of T4 in the first trimester have been associated with decreased IQ and developmental abnormalities in some studies. As well, a recent study of women with subclinical hypothyroidism (meaning high TSH, normal free T4) found an increased risk of placental abruption and preterm birth. Maternal hypothyroidism has also been associated with an increased risk of gestational hypertension and preeclampsia. For these reasons, we increase the dose of thyroid hormone in pregnancy, and follow the thyroid function tests in pregnancy.

   As well, one would want to not only avoid hypothyroidism in a woman with thyroid cancer, but maintain her TSH in the suppressed range. Usually patients are followed every 6-8 weeks until 20 weeks, then every trimester. There is no increased risk to the fetus if a woman has a suppressed TSH, but normal free T4.

   No (special foods or diet is necessary while pregnant). A certain amount of carbohydrates (approximately 175g/day) is recommended as part of a healthy diet during pregnancy. One can choose `healthier' carbs such as those high in fiber.

   Women can safely take thyroid medication while nursing. Women are usually put back to their pre-pregnancy dose immediately after delivery, and their thyroid function tests are checked 6-8 weeks postpartum.

   It is not safe to resume breastfeeding after RAI treatment as the iodine stays in the mother's body for quite a while.

   Pregnancy is an absolute contraindication to radioiodine therapy. Fetal thyroid tissue concentrates iodine after the eighth week of gestation and would be destroyed by the radioiodine, resulting in cretinism.

   Studies show there is no risk to delaying the initial surgery and RAI that follows, so one would assume that there is no risk delaying the RAI till after delivery.

   There appears to be no harmful impact of radioiodine therapy on a woman's fertility, with the exception of one study which found a small increase in the rate of miscarriages in women who became pregnant during the first year post therapy. Other studies, however, have not confirmed this finding. Whether the increased incidence of miscarriages within the first year relates to gonadal irradiation or to insufficient control of hormonal thyroid status is still not known.

   It is recommended that women wait approximately 1 year after radioiodine therapy before becoming pregnant. This recommendation likely stems from the study which showed an increased incidence of miscarriage during the first year after RAI therapy and the concern that persistent effects of radiation MAY cause cytogenetic damage for several months. Waiting one year will also give the physician time to investigate whether the cancer is no longer present, and will allow the patient's thyroid status to be adjusted to the appropriate level. Other studies, however, have not found an increase in miscarriages or adverse neonatal outcomes in women who received iodine therapy within the first year.

   In a patient who has undergone RAI therapy for thyroid cancer, is there an increased risk of genetic and chromosomal abnormalities to the children?

   No. Genetic and chromosomal abnormalities due to exposure to 131-I probably occur in only one percent of live births after a cumulative dose of 500 mCi (18500 MBq), and even less frequently after lower doses. (The average dose given to ablate the thyroid after total thyroidectomy for thyroid cancer is 100 mCi).

   If a patient is discovered to have thyroid cancer during pregnancy, are there risks of thyroid cancer to the fetus?

   In most cases the answer would be no. Familial (genetically inherited) well-differentiated thyroid cancer is very rare.

   In a study of women who received 131-I therapy for thyroid cancer before age 45 year, menopause occurred on average 1.5 years earlier than in women with nodular goiter treated with equivalent doses of T4 (Ceccarelli 2001).

5. What effects does thyroid cancer have on the menstrual cycle and/or on the onset of menopause?

   Driedger (May 1/06, revised Sept 26/08)

   Hypothyroidism does indeed disturb the menstrual cycle. Typically, it results in a heavier and more prolonged menstrual flow for that cycle. This is attributable to the absence of thyroid hormones at the time. In the past it was felt by experts that the total experience of hypothyroidism and radiation therapy would cause some women to miss some menstrual periods and, in the event of pregnancy, that there was an increased incidence of spontaneous abortions in the first year following.

    

   It is not infrequent that women in the later reproductive years stop menstruating after RAI therapy. Maybe it is a little more than coincidence. I don't know of a study that addressed the situation.