The study was funded by AstraZeneca.
A diagnosis of breast cancer can lead to depression, but some antidepressants used with the chemotherapy drug tamoxifen can double the risk of the cancer returning.
Tamoxifen, which interferes with the production of estrogen needed by many tumors, has been used for more than 30 years to prevent tumor recurrence in breast cancer patients and for 10 years to prevent breast cancer in women at high risk. Antidepressants also frequently are prescribed, not just for depression but to limit the hot flashes that estrogen deprivation can cause.
Tamoxifen is activated inside the body by a liver enzyme called CYP2D6. Some antidepressants, such as Paxil, Prozac and Zoloft, are moderate-to-potent inhibitors of this enzyme. Others, such as Celexa, Lexapro and Luvox, are weaker inhibitors. Laboratory studies have suggested the potential for harmful interactions between all of these antidepressants, known as selective-serotonin re-uptake inhibitors, and tamoxifen.
Researchers at Medco Health Solutions Inc., a pharmacy benefits company in Franklin Lakes, N.J., searched their medical and drug records of more than 10.7 million people to identify women who were taking one or both drugs. They found 945 women taking tamoxifen and 353 taking tamoxifen and an SSRI.
Dr. Robert Epstein, the chief medical officer at Medco, told the ASCO meeting that women taking Paxil, Prozac or Zoloft in combination with tamoxifen had a 16 percent risk of breast cancer recurrence compared with a 7.5 percent risk among those taking tamoxifen alone. Those taking other antidepressants in the same family had a 14 percent risk of recurrence.
In an e-mailed statement last week, Food and Drug Administration spokeswoman Karen Riley said that the agency probably will revise the tamoxifen label to warn women and doctors against using SSRIs in conjunction with it. Epstein said his company is notifying doctors. Some doctors have switched patients who need an antidepressant to Effexor, which seems to be less harmful.
About 187,000 American women are diagnosed with breast cancer each year, and 41,000 die from it. The study was financed by Medco.
