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The Genetics of Breast Cancer

Susan C. Stewart, M.D.
 
Everyone of us has had a friend or relative concerned about their family history of breast cancer. This is totally understandable given that breast cancer is the commonest cancer in women and is the third most deadly cancer in men and women behind lung and colorectal cancer. What's more, with the media's emphasis on a woman's one in eight chance of developing breast cancer during her lifetime, an alarming figure, women should be concerned!

But there are two pieces of good news. First, with the greater use of mammography and diagnostic techniques that permit diagnosis at earlier stages, the cure rate is improving. Second, the one in eight risk isn't as high as it seems. It's a lifetime risk, what we call cumulative risk, based on a woman living to the ripe old age of 110. A woman's risk at age 50, for example, is much lower, 1 in 50. (see Table 1)

Table 1.
A Woman's Risk of Developing Breast Cancer by Age
By age 25 one in 19,608
By age 30 one in 2,525
By age 35 one in 622
By age 40 one in 217
By age 45 one in 93
By age 50 one in 50
By age 55 one in 33
By age 60 one in 24
By age 65 one in 17
By age 70 one in 14
By age 75 one in 11
By age 80 one in 10
By age 85 one in 9
Ever one in 8
source: NCI Surveillance Program


Two Kinds of Inheritance
Most cases of breast cancer, about 90%, result from one or more mutations, mistakes made while the cells are dividing in the breast tissue. We're not sure what causes these body cell ("somatic") changes — what you eat, where you live, passing cosmic rays have all been suggested as culprits.

Another 10% of breast cancer is associated with specific inherited mutations. So far, we've identified two genes, the BRCA1 or the BRCA2, which are passed from generation to generation with mutations for breast cancer already in them. A practical consideration from this knowledge is that a woman with a BRCA1 gene mutation in her family, who tests negative for that mutation, is not without risk for breast cancer. She still faces the one in eight lifetime risk for a somatic mutation and should continue surveillance accordingly.

Both BRCA1 and BRCA2 mutations confer increased risk for breast and ovarian cancer as well as for other cancers. They are tumor suppressor genes — when mutations alter or inactivate this function, cancer is more likely to develop. These genes were discovered through studies of families with multiple cases of breast cancer in different generations. Table 2 summarizes key information about the effect of mutations in these two genes.

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Readers Comments
(2) Comments have been made

Devon
Good information for my mini symposium on genetic disorders. Thanks a lot.
Posted Sat, Jan. 9, 2010 at 10:59 am EST
 
maggie
this website was alot of help for a prodject thanks
Posted Tue, Jan. 5, 2010 at 7:46 pm EST



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