Cancer patients with underactive thyroid hormone (hypothyroidism) sometimes live longer than those with normal thyroid function-but, until recently, oncologists didn't know why.
What has been discovered?
In a study where a hypo (low) thyroid state was induced in patients with recurrent gliomas (aggressive brain tumors), their survival rates were about three times longer than those patients with the same cancer who had normal thyroid function, says Aleck Hercbergs, MD, a radiation oncologist at the Cleveland Clinic. It appears that thyroxine, the body's main thyroid hormone, may stimulate cancer cell growth.
Interestingly, when the charts of nearly 2,000 lung cancer patients were reviewed, those with a history of hypothyroidism were diagnosed at an average age that was 4.3 years older than those with normal thyroid function-suggesting that these cancers took longer to grow to a diagnosable stage. Similar patterns have been noted in patients with breast and kidney cancers.
Even though the link between thyroid hormone and cancer growth is still speculative, some doctors now advise hypothyroid patients with an active cancer (or a history of cancer) to use the lowest possible dose of thyroid hormone replacement—or forgo it altogether. Cancer patients may want to ask their oncologists if thyroid manipulation—using available drugs to artificially create a low-thyroid status-though experimental, might improve their outcomes.
On the horizon: A hormonally inactive chemical byproduct of thyroxine may help prevent cancer cells from proliferating-perhaps leading to new anticancer drugs.
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