Pfizer Inc.'s kidney cancer drug Sutent may increase the risk of hypothyroidism, a condition that causes fatigue and weakness, a study said.
As many as 85% of patients taking Sutent for kidney tumors had blood tests showing abnormal thyroid activity, according to a study yesterday in the Journal of the National Cancer Institute. Among those with positive blood tests, 84% had signs or symptoms of the disorder, the researchers reported. Doctors should routinely monitor thyroid levels of patients taking Sutent, known by the chemical name sunitinib, so they can treat irregularities, the study of 66 patients said.
Sutent had sales of $115 million as of October 1 last year, the most recent data available from New York-based Pfizer Inc. Hypothyroidism „is an easy thing to fix,” said Brian Rini, the study's lead researcher and a cancer doctor at the Cleveland Clinic. Rini said patients with symptoms can be treated with the drug, Synthroid, a hormone replacement drug sold by Abbott Laboratories. About 25% of patients in the study chose to take a hormone replacement medicine to treat the condition and about half of those saw an improvement, he said.
Sutent's prescribing information already contains an advisory to doctors that 7% of kidney cancer patients in studies experienced hypothyroidism. „This is an easily managed lab abnormality,” said S. Hariharan, Pfizer's medical director for Sutent, in a telephone interview today. „Hypothyroidism is well know and Synthroid had been around for many decades so if it was an abnormality doctors will be able to monitor it and treating it.”
Pfizer is conducting its own studies to determine if the drug has an impact on the thyroid gland, Hariharan said. Researchers at the Cleveland Clinic said they began studying the thyroid levels of Sutent users after fatigue, a symptom of hypothyroidism, was reported as a common side effect of the drug. Hyperthyroidism is caused when the thyroid gland, located in the neck, doesn't produce enough of the hormones that regulate the body's use of energy, according to the US National Institutes of Health.
The researchers said that because they didn't include a control group not taking the drug, the connection between Sutent and low levels of the thyroid hormone may be due to other factors. Rini said it was unlikely the irregular thyroid activity was caused by the cancer. The drug was approved by the US Food and Drug Administration (FDA) in January 2006 for treating a form of kidney cancer called metastatic renal cell carcinoma, and certain stomach tumors.
Sutent belongs to a new class of cancer medicines, which include Bayer AG's Nexavar, that shrink tumors by choking off a tumor's blood supply. One possible reason for the under-active thyroid in Sutent users may be that the drug also cuts off the blood supply to the thyroid glad, Rini said. Last quarter, Nexavar sales were outpaced by Sutent as Q3 sales grew 41%, while revenue from Sutent rose 75%, according to a note from HVB Group analyst Andreas Heine. Guenter Forneck, a spokesman for Leverkusen, Germany-based Bayer, couldn't immediately say if Nexavar's effect on thyroid function has been investigated to date. (Bloomberg)