underactive thyroid and breast cancer

I have recently been diagnosed with an underactive thyroid and wondered if anyone else has had the same problem. I am taking Arimidex. It’s just researching it apparently a percentage of thyroid sufferers get breast cancer and I wondered if it was really the other way round. I know that radiotherapy to the thyroid can cause it and wondered if it was to do with the radiotherapy I received for breast cancer.

Pollyt hi I’ve got a underactive thyroid but have had it for 20 yrs so unsure if linked to bc as prim was 09 tc laura

Hi Polly,
interesting question, I have underactive thyroid, but wasn’t diagnosed with that till after cancer (though I guess I could have had it before and not known). Also have a friend and my sister who have both bc and thyroid,looks like there may be some link but which way?!

wish i hadnt read this now my daughter has a thyroid problem and told me the other week she found a lump in her breast too i have told her to get it looked at just hope its nothing as she is trying so hard to start a family

I have an underactive thyroid but have had it for about 8 years and was diagnosed with bc July 2010 but since I have been taking arimidex it as gone the other way overactive so the GP is decreasing the thyroid meds to try to get it back nearer normal am wondering if it could be the arimidex that caused it to change,

I was diagnosed with an overactive thyroid a year before BC. I queried whether these were related, both with the oncologist and the thyroid clinic, and they all said no.

I think many thyroid problems appear in middle age, especially underactive thyroids and middle aged women - and of course this is also when BC starts to appear, so although the two conditions may be related, it is probably just that both conditions happen to occur in middle aged women.

i have had an underactive thyroid for years. I am on thyroxin. i get tested every year, and they recommend reducing the dose, but i feel better on a slightly higher dose and they are fine with that.

Of course everyone who answered this link is going to have an underactive thyroid. It would be interesting to know how many on the site do not have the condition. i might start another thread

I have an under active thyriod, have had it for over 16 years, Bc only diagnosed Feb 11, wonder if there’s a link ?


I discovered that I had an under active thyroid during my radiotherapy. I had visited my GP for blood tests to check my cholesterol etc and when the results came back she said that my thyroid was very underactive, and had I not noticed any symptoms - I thought I was just exhausted from all my treatment. I asked the radiographers if this could have been caused by the radiotherapy and they told me that sometimes it can affect the thyroid gland if given to that region of the body, but could not be sure. It runs in my family, my father and sister have both got an underactive thyroid so I guess I will never know if I inherited it or if it was brought on by the chemo or radiotherapy.

Tbh I think it’s just luck if that’s the right word I was in my 20s when they found out I had a underactive thyroid so don’t really understand if it’s linked as prim bc dx 09 a long way off from dx but I cld just be diff

I had a mild goitre diagnosed 14 years ago. I picked up on it as I noticed I could only see one of the two bones at the front of my neck.
The strange thing is that around 15 months ago I noticed that the goitre had disappeared and I could see both bones again. Ten months later I was diagnosed with BC. Maybe a coincidence but it has been on my mind since diagnosis.


I have had a slight goitre for many years. About 10 years ago, I noticed it had enlarged and was referred to an endocrinologist who did a radio iodine test. The diagnosis was thyroiditis. Only 10% of the thyroid was functioning normally, but that 10% was producing enough thyroid hormone so that I didn’t need to take thyroxine.
I wonder if there is a link or if this is just coinicidence.
Has anyone seen anything in the science/medical journals?

I was diagnosed with an underactive thyroid about 8 years ago and I am being treated with thyroxine everyday, then 5 years ago developed breast cancer, 2 ops, chemo and rads and then 18 months ago diagnosed with secondary in lung and being treated with letrozole (femara). I must admit I have often wondered about the connection with thyroid problems as my mum also had an underactive thyroid and got cervical cancer, which she died of at 51, that was 30 years ago and treatments were very limited, It has always crossed my mind though if there is a connection with thyroid disfunction or just a coincidence.

Take care all
Love Marina x

Hello girls.

Many studies have shown a link between thyroid disfunction and breast cancer, especially where the thyroid problem is a reuslt of an autoimmune disease such as Hashimoto’s.

There are conflicting results in the medical literature. It was a while ago that I read it but I seem to remember that there’s a very good paper from UCLA outlining a possible link. Interestingly,both the thryroid and breast tissue uptake iodine.

Age 46
Dx Hashimoto’s 1990,
Dx IBC Jan2010. ER/PR neg HER2 pos, grade 3, spread to seven nodes,

i was diagnosed with underactive thyroid 6 years ago i also am wondering if there is a link with bc and thyroid problems ?

I also have a underactive thyroid have had it for about 15 yrs now was dx with bc 2 yrs ago then sec to lungs in march seems there are a few of us maybe I’ll ask onc when I next see him

There does seem to be a lot of ongoing research on a possible connection. However both hypothyroidism and breast cancer are fairly common conditions so there is liable to be some overlap anyway.
Signed another BC and hypothyroid one.

Thyroid problems and breast cancer are, sadly, very common. My surgeon, oncologist and endocrinologist all insist there is no link between my radioactive iodine treatment for Graves Disease and subsequent breast cancer.

Me too, underactive thyroid,thyroxine. The more you read the more you realise that the little butterfly shaped thyroid gland affects most of our body functions.