RISKI ANLAMA
Smoking is associated with an increased risk of breast cancer as well as other diseases.
Suppose your risk of breast cancer is 14%. If you smoke, your risk goes up by 32% (about a third higher risk). That means your risk of breast cancer from smoking is 32% higher than the 14% risk if you don't smoke. That's the relative risk increase from smoking.
But how big a difference does a 32% increase really make for you? To figure out the change to your absolute risk, see what happens when you make your risk of 14% go up by a third:
- Multiply your risk of 14% by the relative risk increase of 32%. You get 4% (14% x 32% = 4.48%, or 4%). 4% is the size of the increase in risk.
- Add the 4% increase to the 14% risk you started out with, and you end up with 18% risk (14% + 4% = 18%).
That means your absolute risk for breast cancer is 18% if you have no history of the disease and you smoke.
Example of risk going down for a woman with breast cancer history
Suppose you have had breast cancer and had lumpectomy with clear margins (meaning no cancer was found between the tumor and the edge of the surrounding tissue that was removed along with it).
After lumpectomy with clear margins, your risk of the breast cancer coming back in the same breast is about 30%. But if you choose to have radiation therapy after your lumpectomy, you can reduce your risk of the cancer coming back by two-thirds, or 66%. This is the relative risk decrease.
But how much of a difference does radiation's 66% drop really make? To figure out the change to your absolute risk, take two-thirds off your risk of 30%:
- Multiply your risk of the cancer coming back (30%) by the relative risk decrease from radiation therapy (66%), and you get a decrease of 20% (30% x 66% = 19.80% or 20%).
- To figure out your remaining risk of recurrence after radiation, subtract the 20% from the 30% risk of recurrence that you started out with (30% - 20% = 10%). So your absolute risk of the cancer coming back falls to 10% if you have radiation therapy.
Now, after lumpectomy and radiation, is there something else you can do to knock down the 10% risk further? You may also choose to take hormonal therapy (for example, tamoxifen or an aromatase inhibitor) for 5 years. If you do that, you can reduce your risk by another 50%. By taking hormonal therapy for 5 years, you lower your relative risk of the cancer coming back in the same breast by half, or 50%. To see how big a difference hormonal therapy makes in your absolute risk, take half off your risk:
- Multiply your risk by the relative risk decrease from tamoxifen (10% x 50% = 5%).
- Then subtract that 5% from your risk (10% - 5% = 5%).
Now your absolute risk of the cancer coming back is 5%. So by having radiation therapy and taking hormonal therapy for 5 years, you have reduced your risk of the breast cancer recurring from 30% to 5%.
Knowing how much your breast cancer risk changes with lifestyle changes and treatment options can help you and your doctor make the best decisions for YOU.