Hyperthyroidism and BC...relation?

Rushell

I have been told that hyperthyroidism can put you at higher risk for breast cancer.

I have been trying to find more information out there regarding this but it seems that there is a bit of a debate on that very subject out there in the "Google" world.

I have had hyperthyroidism for almost 20 years after my first son was born. After finding my lump recently and noticing nipple discharge....my doctor also tested my thyroid to find that my thyroid results "were out of wack". my test results showed a .23 which is extremely low. Normal range should be anywhere from .4 - 4.2. I will be going back in 6 weeks to have it checked again.

Does anyone know where i can find some info regarding hyperthyroidism and it's relationship to breast cancer? Thanks.

leaf

Well, both thyroid disorders and breast cancer are relatively common disorders.  So it would not be uncommon to have both, just by chance (if they are independent diseases).

This study found an association, but it may be just chance. http://www.ncbi.nlm.nih.gov/pubmed/20354521.  This1997 paper opined the association has long been a matter of debate. http://www.ncbi.nlm.nih.gov/pubmed/9240623

This study speculated a possible hypothetical mechanism. http://www.ncbi.nlm.nih.gov/pubmed/18676157

Since they don't even know if the association is real, the association, if real, is quite weak.

Breast cancer prediction models for individual patients are in their infancy.  

When you look at breast cancer risk models, the most popular (for women withOUT a personal history of breast cancer, DCIS, or LCIS) is the Gail model. http://www.cancer.gov/bcrisktool/

However, you must look at the caveats about that model. 

The Gail model specifically says it should NOT be used for medical decisions.(All other models I have seen, with the possible exception of BRCA  models - are just as rotten as the Gail model for prediction of breast cancer for an individual woman.)

For example, this medical journal opines that, even for the 'average' women, the Gail model, and other models that include significant risk factors are, for any individual woman, "better than the toss of a coin, but not by much".  http://jnci.oxfordjournals.org/cgi/reprint/98/23/1673.pdf

That's because when they compared any randomly selected woman WITH breast cancer, and compared her score to any randomly selected woman WITHOUT breast cancer, roughly 55-60% of the time, the woman WITH breast cancer got a higher score than the woman WITHOUT breast cancer.  However, this means that about 40-45% of the time, the woman WITHOUT breast cancer got a higher score than the randomly selected woman WITH breast cancer.  This is even when they threw in known, established risk factors such as breast density.

So, yes, there may be an association between thyroid disorders and breast cancer. I have both a thyroid disorder and LCIS, which is usually considered a risk factor for breast cancer.

I certainly wouldn't worry that your thyroid disease means you are destined you will get breast cancer.  There are many risk factors for breast cancer that are a lot stronger than thyroid disease (in populations), yet they still are not powerful enough to separate out individual women who will get breast cancer from those that won't.