BRCA1 and BRCA2 Risk Stats Simplified

I accepted long ago that my brain is wired for language, not numbers. All forms of math befuddle this word nerd. In the quest for knowledge about cancer risk, information in the form of numbers cannot be avoided. If those annoying stats were not so central to the BRCA decision-making process I’d vote to toss them out the window. In college I learned that statistics do not lie, but people do. Statistical data can be slippery and open to interpretation.

Here is a breast cancer statistic that is commonly repeated:

1 in 8 women will get breast cancer in their lifetime. What does that statement really mean? Breast cancer risk varies greatly throughout the course of one’s life according to the National Cancer Institute.

A woman’s chance of being diagnosed with breast cancer is:

from age 30 through age 39 . . . . . . 0.43 percent (often expressed as “1 in 233”)

from age 40 through age 49 . . . . . . 1.45 percent (often expressed as “1 in 69”)

from age 50 through age 59 . . . . . . 2.38 percent (often expressed as “1 in 42”)

from age 60 through age 69 . . . . . . 3.45 percent (often expressed as “1 in 29”)

Source: web site

Do you see 1 in 8 here anywhere? Nope. The one in eight number comes from looking at all women in the population up to age 80. This is an example of absolute risk. Let’s save relative risk for another day before I fall asleep writing this.

When it comes to absolute risk for BRCA positive people, the numbers that get tossed around can vary widely. They are often shown as a range. Keep in mind genetically inherited BRCA cancers strike differently in one family versus another. Some families will get more cancer than others and we do not know why this is so. Your family might fall at the low end of the range. Or not. This is part of why genetic counseling is a critical part of the BRCA learning curve. Those genetic counselor geeks know how to analyze numbers that are applicable to your situation.

One of the better examples of showing BRCA cancer risk as an easily understood graphic that I’ve seen comes from the new Basser Research Center for BRCA1 and BRCA2 at the University of Pennsylvania.

For this math loser, here is data I can digest and easily repeat to others. Why? Everyone understands basic percentages. In the general population, roughly 13 women out of 100 will get breast cancer at some point in their lives if they live to be 80 years old. For every 100 women who have a BRCA1 mutation like me, between 60 and 80 of them will get breast cancer if they live to age 80. Numbers like these matter when one is trying to decide whether to chop off precious body parts.

I will place these well organized numbers in my KISS (Keep It Simple Stupid) file for a book about cancer I’d like to write one day. Even if I never do fully understand the metric system or dividing fractions at least I can explain to my hairdresser why I’m having more surgery soon.


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