Concern about Paxil’s effect on breast cancer risk misses larger point

March 4, 2014 | by

A new test that allows researchers to quickly identify drugs and chemicals that could disrupt the balance of hormones in the body – potentially affecting development and progression of cancer, including breast cancer – has raised worries about the common antidepressant Paxil.

Antidepressants are a common therapy to combat depression in cancer patients. A new assay that found one antidepressant raises questions that should be researched, but no one should stop medications without consulting a doctor.

Antidepressants are a common therapy to combat depression in cancer patients, but a new assay that found one antidepressant, Paxil, could have an estrogen-promoting effect. That same assay found that other common drugs could have an estrogen-inhibiting effect. City of Hope's Joanne Mortimer urges women and their doctors to focus on the larger picture.

In a trial screening of 446 common drugs, paroxetine – commercially known as Paxil – was found to have a weak estrogen-boosting effect, while other drugs were found to have slight estrogen-inhibiting effects. The implications for such an assay – developed at City of Hope – are significant, but it was the Paxil finding that grabbed national media attention. With 12 percent of Americans age 12 and older taking some form of antidepressant, the study and ensuing coverage raised concern among many women that Paxil might promote the growth of breast tumors.

A City of Hope women's health expert says the new research has a larger message. The message isn't that women should stop important medications – but rather that scientists and physicians should focus on increased opportunities for breast cancer research.

 “They’re very important drugs from a quality-of-life standpoint,” said Joanne Mortimer, M.D., director of Women's Cancers Programs at City of Hope. “No drug has a single effect on the body. Every drug has many different effects. It’s really important to know that, and to be able to measure this in the laboratory, but ultimately we don’t know at this point what impact they have on breast cancer. What comes out of the lab isn’t the same as what happens when you put this in the human body.”

The novel assay – developed at City of Hope and the topic of a paper in an upcoming issue of Toxicological Sciences – allows 1,536 compounds to be tested at once, opening up new avenues for research, including breast cancer research. The assay also found that two antifungal medications – biconazole and oxyconazole – can lower estrogen levels, similar to some medications prescribed to prevent breast cancer and breast cancer recurrences.

Previous studies had also indicated that Paxil has an endocrine-disrupting effect, including a 2010 study conducted in Canada. Mortimer said Paxil generally is not currently prescribed to women with breast cancer, but other drugs in the same family sometimes are.

A key benefit of the new assay, developed by Shiuan Chen, Ph.D., chair and professor of Cancer Biology at City of Hope, is that it allows many compounds to be tested rapidly and at once, giving doctors and researchers a wealth of new information to consider, and opens potential avenues for human studies.

 “I don’t know how much to be concerned about this just yet, though the findings are provocative,” Mortimer said. “We find clues in the lab, but testing them in people is really important … There are so many things that contribute to the risk of cancer. Not everyone who smokes gets cancer – and yet, smoking is the number one known cause of cancer. It’s a very complex disease.

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Learn more about breast cancer treatment and research at City of Hope.