Risk going down

Example of breast cancer risk going down

Suppose you have had breast cancer and undergone lumpectomy (removal of the tumor itself and a margin of healthy surrounding tissue). The absolute risk of the breast cancer coming back in the same breast is about 25%. But if you have radiation therapy to the remaining breast tissue, you can reduce that risk by about 60%. To describe this relative risk decrease, your doctor might say:

Compared to women who have lumpectomy alone, you have a 60% lower risk of developing breast cancer again in the same breast if you have radiation therapy after lumpectomy.

Medical researchers might express it this way:

Compared to women who do not have radiation therapy, your relative risk of developing breast cancer is .40 (1 – .60 = .40). Again, the number “1” is assigned to the baseline group, which is not taking the extra action to decrease the risk. The .60 is subtracted from 1 because it represents a decrease in risk. In other words, you have about 40% of the risk of developing breast cancer again in the same breast as they do.

So in this scenario, what difference does radiation therapy really make for you in terms of reducing the absolute risk of cancer recurrence in the same breast? To know that, you have to multiply the risk of recurrence without radiation (25%, or .25) by the relative risk of .40:

.25 X .40 =.10. In this hypothetical situation, your absolute risk of the cancer returning in the same breast is 10%, or 1 in 10, if you have radiation therapy, versus about 25%, or 1 in 4, if you don’t. Put another way, 1 in 10 women who have radiation therapy can expect to experience recurrence in the same breast, versus 1 in 4 women who do not have the treatment.

So, relative risk is the number that tells you how much something you do, such as a certain behavior or treatment, can change your risk for breast cancer compared to those who don’t do it. A relative risk of:

.5 means that your risk decreases by half, or 50%

1.88 means that your risk increases by 88%

3.0 means that your risk triples, or goes up by 300% (you have three times the risk)

As the examples above show, knowing how much your breast cancer risk goes up or down with certain lifestyle factors and treatment options can help you and your doctor make the best decisions for you. These are hypothetical examples; you can find out more about breast cancer risk in the Lower Your Risk section.



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