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Breast Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Overview

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Magnitude of Effect: After a median follow-up of 35 months, women aged 35 years and older who had at least one risk factor (e.g., women aged 60 years and older or those having a Gail 5-year risk >1.66% or ductal carcinoma in situ with mastectomy) and who took 25 mg of exemestane daily were less likely to be diagnosed with invasive breast cancer (hazard ratio [HR], 0.35; 95% CI, 0.18–0.70). The absolute risk reduction was 21 cancers avoided out of 2,280 participants over 35 months (number needed to treat [NNT], about 100).

Study Design: One randomized controlled trial.
Internal Validity: Good.
Consistency: One study in women with no history of breast cancer, but consistent with RCTs in women with history of breast cancer.
External Validity: Good for women who meet inclusion criteria.

Aromatase inhibitors or inactivators: Harms

Based on fair evidence because of a relatively short follow-up from a single RCT of 4,560 women over 35 months, exemestane is associated with slightly increased hot flashes (absolute increase, 8%) and fatigue (absolute increase, 2%), but not with fractures, osteoporosis, or cardiovascular (CV) events compared with placebo.

Magnitude of Effect: There was a small increase in adverse effects in the exemestane group compared with placebo, primarily in hot flashes (absolute increase, 8%) and fatigue (absolute increase, 2%). There was no difference in the occurrence of fractures or CV events.

Study Design: One randomized controlled trial.
Internal Validity: Good.
Consistency: Poor, as there is only one RCT in women with no history of breast cancer, but studies in women with breast cancer have shown decreased bone mineral density and increased fracture rate compared with tamoxifen.
External Validity: Good for women who meet inclusion criteria, but only for 35 months.

Prophylactic mastectomy: Benefits

Based on solid evidence, bilateral prophylactic mastectomy reduces the risk of breast cancer in women with a strong family history.

Magnitude of Effect: Risk is reduced as much as 90%, but published study designs may have produced an overestimate.

Study Design: Evidence obtained from case-control and cohort studies.
Internal Validity: Good.
Consistency: Good.
External Validity: Good.

Prophylactic mastectomy: Harms

Based on fair evidence, physical and psychological effects include anxiety, depression, and impaired body image.

Magnitude of Effect: Of the women who chose to have a prophylactic mastectomy, usually for cosmesis, 6% were dissatisfied with their decision. Regrets about mastectomy were fewer in 185 women who opted not to have reconstruction than in 111 women who chose to have it.[3]

Study Design: Convenience sample.
Internal Validity: Good.
Consistency: Good.
External Validity: Good.

Prophylactic oophorectomy or ovarian ablation: Benefits

Based on solid evidence, prophylactic oophorectomies in women with BRCA gene mutations document lower breast cancer incidence. Similarly, oophorectomy or ovarian ablation is associated with decreased breast cancer incidence in normal women or in those who received thoracic irradiation.

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WebMD Public Information from the National Cancer Institute

Last Updated: February 25, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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