Paxil Breast Cancer Risk Seen in New Testing Method

Side effects of the antidepressant Paxil may increase the risk of women developing breast cancer, according to a new testing method designed to detect cancer-causing drugs.  

Researchers from the City of Hope cancer research center indicate that a new test called the AroER Tri-Screen, designed to look for drug side effects that could cause cancer, found a potential link between Paxil and breast cancer.

The findings were published ahead of print online in the medical journal Toxicological Sciences. The test looks for endocrine disrupting chemicals that can interfere with metabolism, hormones and biosynthesis. These include the hormones estrogen and androgen.

Researchers found that Paxil has a weak estrogen effect that could increase women’s breast cancer risks. The test has also indicated that the plastic additive Bisphenol A (BPA) and the antifungal drugs Oxistat and Canespor may increase cancer risks as well.

“Approximately 70 percent of breast cancers are sensitive to estrogen, and exposure to estrogen-disrupting compounds — especially during the critical periods of pregnancy, childhood and adolescence — can have an irreversible impact on still-developing babies,” lead author Shiuan Chen, Ph.D., and chairman of City of Hope,s Department of Cancer Biology, said in a press release. “Thus, it makes sense to develop this test, which can assess many chemicals at once, to help us quickly identify which environmental compounds are disrupting estrogen functions.”

Those estrogen disruptions can increase women’s risk of breast cancer or promote cancer growth in women who already have the disease, researchers said. And when they put Paxil through the test, they discovered that it had estrogen disrupting effects.

The finding may explain why a 2010 study found that breast cancer patients who took Paxil were more likely to die of breast cancer than patients taking other antidepressants, researchers said.

Paxil Birth Defects

Endocrine disruption can also affect unborn children, and Paxil has been linked to a significant risk of birth defects.

Paxil (paroxetine) is a selective serotonin reuptake inhibitor (SSRI) prescribed to treat depression. Approved in 1992, it has become one of the most commonly prescribed drugs in the United States, generating sales of about $1 billion a year.

In December 2005, the FDA issued an alert in the United States about the risk of birth defects from Paxil, after studies showed the drug could increase the risk of the heart defects when taken during the first three months of pregnancy. At that time, the agency also required GlaxoSmithKline to update the warning label in this country to include information about the pregnancy risks with Paxil.

The company has faced hundreds of Paxil lawsuits in the United States, which were brought on behalf of children who suffered various birth defects and malformations, such as persistent pulmonary hypertension in newborns (PPHN) and other health problems. The complaints alleged that Glaxo purposefully hid test results that would have revealed the risks associated with use of Paxil during pregnancy and misled doctors.

In October 2009, a Pennsylvania jury awarded the family of a three year old child $2.5 million in compensation for birth defects from Paxil, following the first trial in the country. In 2010, it was reported that GlaxoSmithKline set aside $2.4 billion to settle Paxil birth defect lawsuits.