Tamoxifen, the most widely prescribed anticancer drug currently in use, has been proven effective as both a preventive agent and a treatment for breast cancer. These new findings may allay concerns voiced by a number of researchers about a possible association between tamoxifen treatment and clinical depression.
The study's authors base their conclusions on an examination of data from more than 11,000 women enrolled in the National Surgical Adjuvant Breast and Bowel Project's (NSABP) Breast Cancer Prevention Study. Participants were randomly assigned to receive either tamoxifen or a placebo for five years. Enrollment in the trial was completed in 1997; participants are still being followed.
The main aim of this clinical trial was to determine if tamoxifen would reduce the occurrence of breast cancer in women at increased risk of developing the disease. However, looking at the effect of tamoxifen on depression and other quality of life issues was also a focus.
Researchers measured depression in several ways. First, an assessment of the women's depression risk was made at the time they enrolled in the study. Based on whether women said they had a history of depression, used antidepressant medications at any time or felt depressed or sad for extended periods, the investigators classified the women's depression risk level as high (4.7 percent of participants), medium (23.3 percent of participants) or low (72 percent of participants).
In addition, at the start of the study and then at regular intervals over a three-year period, study participants completed a questionnaire designed to determine whether they had experienced symptoms of depression within the previous week. A score of 16 or higher on the questionnaire indicated that a woman could be suffering from depression.
When the questionnaire responses were analyzed, investigators found that equal numbers of women in the tamoxifen and placebo groups had scores of 16 or higher. Episodes of depression were more frequent, persistent and severe among women who were at higher risk for depression based on their medical history. However, tamoxifen treatment had no effect on the development of depression in any of the three risk groups.
"Physicians need not be overly concerned that treatment with tamoxifen will increase the risk for or exacerbate existing depression in women," write the investigators, who were led by Richard Day, Ph.D., of the National Surgical Adjuvant Breast and Bowel Project Biostatistical Center in Pittsburgh.
Furthermore, physicians need not disqualify women as candidates for tamoxifen treatment because they have a history of depression, the researchers say. However, physicians should continue to carefully screen patients for depression and refer them for treatment when appropriate. 
