Relationship Between Breast Cancer and Thyroid Disease

In the month of October, I like to pay special attention to Breast Cancer Awareness, and this week specifically how breast cancer relates to Thyroid disorders, such as Hashimoto’s. Believe it or not, there’s a link with the two. Today I will discuss my top 3 questions:

1. Is there a relationship between thyroid dysfunction and breast cancer?
2. Is there a relationship between thyroid enlargement and breast cancer?
3. Is Thyroid disease associated with an increased risk of breast cancer?

To find the answers to these questions, I went to my favorite medical research website, the National Library of Medicine. Here's what I found:

Question #1: Is there a relationship between thyroid dysfunction and breast cancer?

I found a study where thyroid disease was examined in 102 consecutive Breast Cancer patients, after surgery and before starting chemo or x-ray therapy. This was also studied in 100 age-matched healthy women living in the same borderline iodine-sufficient geographic area.

All participants were tested thoroughly with thyroid ultrasound, serum free T4, free T3, TSH, thyroid peroxidase antibody, and thyroglobulin antibody determination. They also did a fine needle aspiration (aka biopsy) on all nodules and tested estrogen and progesterone receptors. ( I don’t know about you, but I immediately felt sad for these test participants reading through this study. I personally have been through all of these same tests several times, as I am sure many of you have. It’s just not fun!)

The conclusion of the study was thyroid disease in 46% of breast cancer patients, and 14% in the control group. Non-toxic goiter was present in 27.4% of breast cancer patients, and 11% in the control group. Hashimoto’s was found in 13.7% of breast cancer group, and only 2% in the control group. Other thyroid disorders were found in the breast cancer group including 2 cases of Graves’ disease, 2 thyroid carcinoma, and 1 subacute thyroiditis whereas in the control group only 1 case of Graves’ and no other thyroid disorders.

As for the free T4, free T3 and TSH, they were the same in both groups, however the thyroid peroxidase antibody was higher in breast cancer patients at 23.5% vs 8% in the control group.

To sum this study up, this information provides evidence that the overall prevalence of thyroid disorders is increased in breast cancer patients, and thyroid autoimmune disorders, especially Hashimoto’s, account to a large extent of this number. This calls attention to the need for screening for thyroid disease in any patient with breast cancer.

This study also brings me to wonder, which comes first? I wonder, is there is a link with Hashimoto’s BEFORE breast cancer? Does this mean we, Hashimoto’s patients, should be MORE intentional about breast cancer checkups and prevention if we already know we have Hashimoto’s? In my humble opinion, I would think yes based on this data. I mean, why not? If we know there’s a link, it seems wise to be proactive in prevention measures of either disease, right?

Question #2: Is there a relationship between thyroid enlargement and breast cancer?

According to my research, yes. In a diagnostic ultrasound study of 184 breast cancer patients, the mean thyroid volume of breast cancer patients was significantly greater than in the age-matched controls. Also, the number of individual patients with breast cancer having enlarged thyroid glands was significantly greater at 39.7% than the same number in the control group which was only 8.6%.

There was a direct correlation between thyroid enlargement and breast tumor staging. Both mean thyroid volume and % of enlarged thyroids were identical in groups of patients scanned after and before various therapies for breast cancer, as a result, this excluded therapeutic intervention as a cause for thyroid enlargement.

The results of this study indicate a direct relationship between the two disorders, maybe due to a common growth stimulus? This information may highlight the importance of raising the awareness of the coincidence of both disorders. (Which, by the way, is exactly why I’m sharing this information with you!)

Question #3: Is Thyroid disease associated with and increased risk of breast cancer?

To find the answer this question, I found a systematic review and metanalysis. A systematic review attempts to gather all available empirical research by using clearly defined, systematic methods to obtain answers to a specific question. A meta-analysis is the statistical process of analyzing and combining results from several similar studies. My personal interpretation of what that means is, they make sure the combination of gathered data is unbiased and verified to be accurate in comparisons.

Results of this combined research: A total of 21 articles were included in this study. What they found is Hyperthyroidism, thyroid cancer, thyroglobulin antibody (TGAb) levels, and thyroid microsomal antibody (TPOAb) levels were all significantly associated with an INCREASED risk of Breast Cancer, while hypothyroidism was associated with a REDUCED risk of Breast Cancer.

So, if you’re like me, you might be wondering, what if I have the Hashimoto’s antibodies, but am also HYPOthyroidism, do they cancel each other out? Well, nothing I found could clearly answer that question, but what I interpret from this data, is that the reduced risk was for the very small percentage of people who are ONLY HYPOthyroid, but NOT also Hashimoto’s.

In closing, what are 3 action steps you can take today?

• First, how to help yourself: Get regular checkups and Mammograms, at least yearly. Your doctor may want more often if you have questionable test results. Either way, stay on top of your care, early detection is the BEST prevention!
• How to help others with Hashimoto’s like loved ones or friends? Support them with research, attending medical appointments, and reminding them to schedule their checkups. Brain fog and fatigue is common with Hashimoto’s patients and your help in remembering important check ups could save their life!
• How to dig deeper? Check out the website links for the National Library of Medicine. Here are the links to the research I used in this blog: 

  Is there a relationship between thyroid dysfunction and breast cancer? https://pubmed.ncbi.nlm.nih.gov/8772562/
  Is there a relationship between thyroid enlargement and breast cancer? https://pubmed.ncbi.nlm.nih.gov/8772554/ 
  Is Thyroid disease associated with and increased risk of breast cancer? https://pubmed.ncbi.nlm.nih.gov/33633990/ 
  Explanation of what a Systematic Review and Meta-Analysis are: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5903119/

If you feel overwhelmed or stuck, I’d love to help you with one on one coaching sessions to help you navigate the ups and downs of your own Hashimoto’s journey! My job is to walk alongside you, validate your concerns, equip you with tools and resources, and encourage you along your journey so you never feel alone.

Schedule a free consultation with me today so we can discuss your needs. Also, don’t forget to join my Facebook group, also called The Hashimoto’s Connection for community and friends who also have Hashimoto’s, and meet the guests interviewed on the show!

-Sandy Robinson