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Genes Associated with Breast Size Also Linked to Breast Cancer

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About 5% to 10% of breast cancers are thought to be hereditary, caused by abnormal genes passed from parent to child.

Genes are particles in cells, contained in chromosomes, and made of DNA (deoxyribonucleic acid). DNA contains the instructions for building proteins. And proteins control the structure and function of all the cells that make up your body.

Think of your genes as an instruction manual for cell growth and function. Abnormalities in the DNA are like typographic errors. They may provide the wrong set of instructions, leading to faulty cell growth or function. In any one person, if there is an error in a gene, that same mistake will appear in all the cells that contain the same gene. This is like having an instruction manual in which all the copies have the same typographical error.

Most inherited cases of breast cancer are associated with two abnormal genes: BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two). But changes in other genes also are associated with breast cancer. Researchers are learning that other mutations in pieces of chromosomes – called SNPs (single nucleotide polymorphisms) – may be linked to higher breast cancer risk.

A study found seven SNPs that are associated with breast size. Three of these SNPs also are associated with breast cancer. The study was published online on June 30, 2012 by BMC Medical Genetics. Read the abstract of “Genetic variants associated with breast size also influence breast cancer risk.”

The researchers analyzed genetic information from 16,175 women who had submitted a DNA sample to 23andMe, a personal genetics company. The researchers also asked the women to answer questions about their bra cup size and bra band size. By comparing the genetic information to the breast size information, the researchers found seven SNPs that were associated with breast size. Of the seven, three also are associated with breast cancer and three others are strongly linked to estrogen regulation and breast development.

While these results seem worrisome, there are reasons to be hopeful. More than 1,000 abnormal genes may be linked to breast cancer risk. This study doesn’t prove that larger breast size is linked to breast cancer. Instead, it offers one more bit of information to help doctors understand the very complex relationship between breast cancer and the genes that influence breast development and growth.

Doctors are continuing to look for better ways to figure out each woman’s individual risk of breast cancer. The goal is to create a personalized screening and breast health plan tailored to that risk. In the meantime, it’s a good idea to do all you can to keep your risk of breast cancer as low as it can be. You can learn about some steps you can take in the Breastcancer.org Lower Your Risk section.

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