👉The average probability of developing breast cancer by age 70 is estimated at 57% to 59% for BRCA1 gene mutation carriers and 49% to 51% for BRCA2 gene mutation carriers.
👉Emphasis is on the word “average” because these estimates are based on data from families with a lot of breast cancer cases as well as families with very few breast cancers.
👉Previous studies that had only included families with many breast cancer cases had concluded that lifetime breast cancer risk was more in the range of 80% to 85%.
👉This illustrates an important point: the risk conferred by a pathologic mutation in any breast cancer predisposition gene will vary widely by family.
👉This is most likely due to gene-gene interactions, which are the modifying effects of small differences (e.g., polymorphisms) in many different genes.
👉Average risk is a good place to start for any pathologic gene mutation.
👉The “All Syndromes Known to Man,” or ASK2ME, Web calculator is a good place to find average risks for the rarer syndromes (http://www.ask2me.org/).
👉This risk should be adjusted up or down based on evaluation of the three-generation cancer family history.
👉Both age at diagnosis and cumulative risk vary by family.
👉Indeed, even for genes such as ATM and CHECK2, which are thought to be low-penetrance genes, breast cancer risk approaches that of BRCA1 and BRCA2 genes in some families.
👉Careful evaluation of the three-generation cancer family history is required for accurate risk estimation.
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