Text Description: Figure 1. Benefits and Harms¹ of Chemoprevention with Tamoxifen per 10,000 Women in Three Age Groups²

Figure 1 shows the benefits and harms of chemoprevention with tamoxifen for 5 years per 10,000 women in three age groups (40-49, 50-59, and 60-69, respectively) with three color-coded horizontal lines relative to the number of cancer events prevented. Harms in this figure include endometrial cancer, stroke, and pulmonary embolism. Harms vary by age, with older women experiencing more harms than younger women. For women ages 40-49, 44 of 10,000 are likely to experience harms when being treated with tamoxifen, 201 of 10,000 women ages 50-59 experience harms, and 382 of 10,000 women ages 60-69 experience harms.

The benefits vary by estimated risk of breast cancer, so that those at higher risk are more likely to benefit from tamoxifen than those at lower risk. For women in their forties, benefits are likely to be greater than harms. One hundred and thirteen cases of cancer can be prevented among 10,000 women ages 40-49 who have a 1.5 percent estimated 5-year risk of breast cancer, whereas 374 cases of cancer can be prevented among women of the same age who have a 5 percent estimated 5-year risk of breast cancer.

For women ages 50-59, who are at higher risk of harms, the number of cases prevented exceeds the number of women experiencing harms, only when the estimated 5-year risk of breast cancer is 2.5 percent or higher. At a lower level of breast cancer risk, such as a 1.5 percent 5-year risk, 96 cancer events per 10,000 would be prevented, compared with 201 women likely to experience harms.

For women ages 60-69, while tamoxifen does prevent some cancer events, the benefits do not exceed the harms even in women with as much as a 5 percent 5-year risk of breast cancer.

¹Harms include endometrial cancer, stroke, and pulmonary embolism combined.
²Adapted from Gail et al, 1999(49).

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