Your Thyroid Problem and Your Breast Cancer Risk, Part II

Certain common thyroid conditions put women at a higher risk for breast cancer, yet this isn’t common knowledge to even medical professionals.

Why Isn’t It Common Knowledge That Certain Thyroid Diseases Are Associated with Higher Breast Cancer Risk?

The research available on a thyroid disease and breast cancer connection is very, very conflicting, depending on the thyroid disease state and the study being looked at. One study says there are Martians, and other studies say there are not. (Joke.)

How can medical research be so murky? It is frustrating, but I think there are some reasons for it:

One. There is not a direct causal effect between thyroid disease and breast cancer. Having thyroid disease does not cause breast cancer. It’s just that there’s something medical researchers and clinicians haven’t pinpointed with unanimous certainty leading to faulty issues in both organs. Flooding in the basement doesn’t cause my leaky roof; the rain does. (Yes, iodine advocates, I agree. It could be in part a deficit of iodine and its associated necessary co-factors.)

Two. Another problem leading to “research conclusion confusion” in this matter, I believe, is how thyroid disease is diagnosed. About everyone can agree on a TSH (an initial screening thyroid function test), but after that, it starts becoming no-man’s-land about what should be ordered next.

In general, there is an over reliance on TSH, and less monitoring of other thyroid tests, especially thyroid antibodies. Sometimes patients are simply given the diagnosis of “Your-TSH-is-too-high-here-take-this-Synthroid” and little else, if anything, is checked–sometimes not even the thyroid gland itself! I was floored when a newly suspected thyroid patient (a friend) told me the doctor didn’t even feel her thyroid! Another friend, who I sent to go see her doctor for a new goiter (and symptoms of hypothyroidism), was given a good bill of health with no recommendation for close follow-up or any inquiry into her diet; her TSH was normal and so was her ultrasound.

So in the studies, I have to wonder what it means when they say Hashimoto’s, hypothyroidism, or hyperthyroidism. How uniform are the patients in reality? How were all the patients diagnosed? Because so much data was pooled from so many studies for some of the bigger research analysis, it’s hard to say.

Three. Different doctors use different terminology. For example, Hashimoto’s disease can be called 1) Hashimoto’s 2) hypothyroidism or 3) chronic autoimmune thyroiditis (or chronic thyroiditis, autoimmune thyroiditis). Hashimoto’s IS a type of hypothyroidism, but not all hypothyroidism IS Hashimoto’s. However, some doctors will diagnose someone with Hashimoto’s without ordering antibody tests or even imaging. I think some studies aren’t able to tease out how different doctors label thyroid disease differently.

Four. Thyroid fluctuation can also confound statistics. A diseased thyroid will often fluctuate in its function for years, sometimes overproducing thyroid hormone, other times under producing thyroid hormone, and other times managing to make just the right amount of thyroid hormone. Eventually, after years, it may arrive at its final diseased balance. If a patient is monitored at one particular time, they may look completely normal based on TSH. The natural progression of thyroid disease is one of relapsing and remitting changes, sometimes high, sometimes low, and sometimes normal, and I believe this will affect research findings.

Okay. So now that you see reasons why the studies may be so contradictory, let’s look at different thyroid disease states and their breast cancer risk.

The following information may not make sense to you unless you have thyroid disease. Sometimes, even people who have thyroid disease don’t know their specific diagnosis, and this might sound complex even to them. I encourage you, if you have thyroid disease, to know specifically what you’ve been diagnosed with and how that diagnosis was arrived at (TSH, T3/T4 values, imaging, antibody tests, etc.).

Graves’ disease patients seem to consistently show up with higher breast cancer rates. (1, 2, 3)

Hyperthyroidism, not necessarily classified as Graves’ disease, has been shown to have a higher risk of breast cancer. (4)

A patient who has TSHR antibodies (usually diagnostic for Graves’ disease) has an increased risk for breast cancer. (2)

TPO antibodies and thyroglobulin antibodies, commonly found in autoimmune thyroid disorders (Hashimoto’s and Graves’ disease), have been found in some studies to be associated with a higher risk of breast cancer, but in other studies the antibodies were shown to have no relationship, or even an improvement, in the rate of breast cancer.

  • TPO Antibodies:
    • In some studies, TPO antibodies seem to be associated with less risk of breast cancer. (5)
    • Other studies indicate a higher risk of breast cancer with TPO antibodies. (6, 7)
  • Thyroglobulin antibodies:
    • May suggest, but not statistically significant, an increased breast cancer risk. (2)
    • Do show an increased risk for breast cancer. (6, 7)

Nodular goiter and diffuse, non-toxic goiter are associated with an increased risk of breast cancer incidence. (8, 9)

Hashimoto’s or hypothyroidism  (Hashimoto’s usually causes hypothyroidism) patients can take their pick, as there have been reports with no significance in the rate of breast cancer (10), a decreased risk of breast cancer (4), or an increased risk of breast cancer (11).


Okay. I’m reaching my word and reader attention span limit, but I want to tell thyroid patients that this knowledge should not mean fear. Do not be afraid.

This knowledge means vigilance—lovingly tend to your body with good sleep habits, stress management, nurturing connections with friends and family, activity outside in the fresh air, and whole, real food choices rich in vegetables and fruits, and food sources rich in what both the breast and thyroid need.

This knowledge means to talk to your doctor about self-breast exams and mammograms. It means to learn the signs and symptoms of breast cancer, like skin changes and/or nipple discharge. Mammograms and self-exams should probably be more assertive than in a patient with no breast cancer risk factors, especially now as the mammogram guidelines suggest starting later and doing fewer mammograms (which I’m not adverse to that idea necessarily either, but not in patients at known higher risk).

I suggest you know the specific type of thyroid disease you have and whether or not you have antibodies. Doctors think it’s overkill to check antibodies, but if you take in a study that I’ve listed showing an increase in breast cancer with these antibodies, I think a reasonable doctor working with a reasonable patient would order them. I also think that knowing whether or not you’re consuming adequate iodine and iodine co-factors is important. Doctors aren’t well educated on iodine, other than, “Don’t,” and so finding someone who has read some of the newer stuff on iodine insufficiency, women, and breast disease is challenging.

No fear. No anxiety. Awareness. Uncontrolled anxiety does a woman no good. Sure, a little anxiety motivates us. But too much paralyzes us.

The last thyroid and breast post I did discussed thyroid cancer, so if you’re interested, go back and check that one out. Let me know typos, citation issues, or anything else pertinent to the accuracy of this post. Lastly, my blog is not professional advice. Use the citations I list to help you understand your disease better and to help you discuss your own case with your healthcare team better.

The Homeschooling Doctor logoStrength and joy to you all!






1. Johnson RH,  Chien FL, Bleyer A. Incidence of Breast Cancer With Distant Involvement Among Women in the United States, 1976 to 2009. JAMA. 2013;309(8):800-805; doi:10.1001/jama.2013.776.

2. Thyroid-Cancer Survivors at Higher Risk of Breast Cancer. Medscape Web Site. Published June 1, 2015.

3. Nielson SM et al. The Breast-Thyroid Connection Link: A Systemic Review and Meta-Analysis. Cancer Epidemiol Biomarkers Prev. February 2016 25; 231. doi: 10.1158/1055-9965.EPI-15-0833.

4. Sogaard M et al. Hypothyroidism and hyperthyroidism and breast cancer risk: a nationwide cohort study. Eur J Endocrinol. 2016 Apr;174(4):409-14. doi: 10.1530/EJE-15-0989.

5. Itoh K and Maruchi N. Breast Cancer in Patients with Hashimoto’s Thyroiditis. The Lancet. Volume 306, Issue 7945, 6, December 1975, Pages 1119-1121.

6. Turken O, Narin Y, Demirbas S, eta al. Breast Cancer in Association With Thyroid Disorders. Breast Cancer Res. 2003;5(5).


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