How much does preventive mastectomy actually reduce your risk?

For women with a high inherited risk, such as a harmful change in the BRCA1 or BRCA2 gene, removing both healthy breasts lowers the chance of developing breast cancer by a very large amount. Studies commonly describe this as a reduction of around nine in ten or more. That is a relative reduction, which means it is measured against the risk you had before surgery. What it means for you in real terms depends on how high your starting risk was. If your lifetime risk is very high, the drop in absolute terms is large. If your risk is only slightly above average, the same relative reduction removes far fewer actual cancers, and the balance of benefit against the downsides of surgery looks quite different. The risk does not fall to zero, because a mastectomy cannot remove every breast cell. Small amounts of tissue remain under the skin, near the armpit and on the chest wall, and cancer can occasionally develop there. Nipple-sparing and skin-sparing methods keep slightly more tissue, although studies so far suggest the overall protection remains high when done carefully. For women who already have cancer in one breast, removing the other breast lowers the chance of a new cancer on that side, but it does not change the risk of the original cancer coming back or spreading, which is often the bigger concern for survival.

The reduction is large for high-risk women

For BRCA carriers, preventive surgery prevents most breast cancers that would otherwise have developed.

Relative and absolute risk are different

The same percentage means much more when your starting risk is high.

Some risk always remains

A small amount of breast tissue stays behind, so a small chance of cancer remains.

Many people assume that fewer cancers automatically means longer life. The link is real for some groups, but it is not always as strong as expected.

For healthy BRCA carriers

Some studies suggest preventive surgery may improve survival, particularly for BRCA1 carriers, but intensive screening also finds many cancers early, when treatment works well.

For women already diagnosed

The main threat to survival is usually the first cancer spreading, which removing the other breast does not prevent.

For women at moderate risk

Surgery generally has not been shown to improve survival, while its side effects remain.

Peace of mind counts too

For some women, relief from constant worry and screening anxiety is a meaningful benefit in its own right.