Hi. I have hereditary thyroid disease. First it was hyperthyroidism treated with a small amountdof radioactive iodine which only killed off a small amount of thyroid. I eventually ended up with hypothyroidism and have managed this well for a number of years. When having chemo treatment my TSH level went up to 8. (Normal is 0.3 to 4). My normal is between 0.3 and 3. Any higher and I get depressed and tired. So chemo really messed with either my thyroid or thyroid meds. So did anti estrogen drugs. I am only taking 2 tamoxifen tablets a week now and my life and thyroid returning to mormal. You need to get your TSH level tested every 6-8 werks until you get stable. KNOW what your levels are and make sure you get copies of your tests. T3 and T4 also needs testing at the same time. Hint. When you have your blood tests make sure it has been at leadt 6 hrs since taking thyroid meds. You will live a normal life with hypothyroidism. I believe cancer treatments and drugs interfere with thyroid. Don't hesitate to talk to me anytime. Sue