Background: Tamoxifen is an oral anti-estrogen used in the treatment of breast cancer and recently approved to reduce the incidence of breast cancer in high risk women. As a large clinical trial of tamoxifen has reported an increased risk of cataract, we conducted a study of women with breast cancer to evaluate the association of tamoxifen with cataracts and other eye problems.
Methods: We attempted to recruit previously interviewed patients who were cases in a population-based case-control study of 2653 women with primary breast cancer diagnosed between 1987 and 1996 at ages 55-72 years in Los Angeles County, California, USA. In November 1997, each case was mailed a questionnaire to ascertain self-reported incidence of eye diseases and Amsler grid test scores. Information from 1297 women aged 57-75 years of age was analyzed. Women reporting treatment with tamoxifen were categorized as standard-term users (4-5 years), short-term users (<4 years), or long-term users (6+ years) and compared to non-users. All p-values, relative risks, and confidence intervals for differences in eye problems and grid test results are adjusted for age and stage of disease at diagnosis.
Findings: Standard-term and long-term users of tamoxifen more frequently reported developing cataracts than non-users (18.2%, 21.4% vs. 14.8%). The relative risk was 1.40 (95% confidence interval 0.94-2.10) for standard-term users and 1.70 (1.11-2.59) for long-term users. Tamoxifen use was unrelated to frequency of glaucoma or macular degeneration or to Amsler grid test results.
Interpretation: Our study suggests that five or more years of tamoxifen use increases risk of cataracts. Healthy women considering tamoxifen use to reduce risk of breast cancer should be advised of the possibility of cataract development. Women choosing such therapy should be diligent about receiving regular ocular exams.