Study links Paxil to increased breast cancer risk in women

After developing a faster way to identify drugs and chemicals that may disrupt the balance of hormones in the human body, California scientists have fingered the popular anti-depressant drug Paxil and linked it to a possible increased breast cancer risk.

The study, reported by the Los Angeles Times, found that the popular antidepressant Paxil (chemically known as paroxetine) has a weak "estrogenic effect," meaning that it may be responsible for cancers in some women. They compared it against 445 other drugs "in wide circulation," according to the report.

The particular screening method used to detect hormonal changes after exposure to drugs or chemicals is new. The method also identified two other medications -- the antifungals biconazole and oxyconazole -- as having an anti-estrogenic effect. This is in opposition to Paxil, meaning it may reduce cancer or the recurrence of cancer in some women. Estrogen is seen playing a role in the growth and recurrence of cancers.

The study builds upon a finding in another Canadian examination of Paxil in 2010. That study found that breast cancer patients who took Paxil were more likely to die of breast cancer if they took it in concert with tamoxifen, an anti-cancer drug.

In the Canadian study, researchers hypothesized that Paxil might block the production of a liver enzyme needed to metabolize tamoxifen.

A 2012 study conducted in Holland also linked Paxil and other selective serotonin reuptake inhibitors (SSRIs) -- a popular antidepressant class that includes the drugs Prozac and Zoloft -- with increased falls among elderly patients. A 2012 study found Paxil more than doubled the risk of a woman's child being born with a birth defect that affects breathing.

Writes the Times:

Last summer, the Food and Drug Administration approved the marketing of a low dose of paroxetine -- repackaged under the commercial name Brisdelle -- as a nonhormonal treatment for hot flashes and other menopausal symptoms.

About 70% of breast cancers in women are sensitive to estrogen, meaning that the hormone found plentifully in females of child-bearing age contributes to their growth.

The novel screening method... described in a forthcoming issue of the journal Toxicological Sciences, also identified two antifungal medications -- biconazole and oxyconazole -- as having an anti-estrogenic effect similar to that of medications prescribed to prevent breast cancer and its recurrences in women. Incidental to their intended use in combating fungal infections, those medications inhibit the action of aromatase, an enzyme that converts androgens -- hormones more plentiful in males but present in both sexes -- into estrogen...

Less surprising, the high-throughput screening mechanism identified bisphenol A -- a compound used in the manufacture of plastics and epoxy resins -- as an estrogen promoter capable of raising breast cancer risk.

Paxil has been on the market since 1992. According to the Times, almost a quarter of American women in their 40s and 50s take an antidepressant, generally an SSRI.

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