Breast cancer risk: It's not all in the family

Women do not automatically have a higher risk of getting breast cancer just because someone else in the family has tested positive for breast cancer genes, U.S. researchers said Monday.

The findings may bring comfort to women from high-risk families after a 2007 study suggested that simply having a relative with a BRCA1 or BRCA2 mutation raised their risk of developing breast cancer, even if they had tested negative for the genes.

"The results are encouraging and reassuring," said Dr. Allison Kurian of Stanford University School of Medicine, whose study appears in the Journal of Clinical Oncology.

The average woman in the United States has about a 12 to 13 percent chance of developing breast cancer in her lifetime.

Some 5 percent to 10 percent of breast cancers are genetic, and most of these cases are caused by abnormalities in the BRCA1 or BRCA2 genes.

Women with these mutations have a five to 20 times higher risk of developing breast or ovarian cancer, and must undergo intensive cancer screenings and take other precautions to reduce their cancer risk.

Risk Factors for Breast Cancer

In 1940, the lifetime risk of a woman developing breast cancer was 5%, or one in 20. The American Cancer Society estimates that risk to be 13% in 2009, or almost one in eight. In many cases, it's not known why a woman gets breast cancer. In fact, 75% of all women with breast cancer have no known risk factors.

What Are the Risk Factors of Breast Cancer?
A risk factor is anything that increases a person's chance of getting a disease. Different cancers have different risk factors.

But having a cancer risk factor, or even several of them, does not necessarily mean that a person will get cancer. Some women with one or more breast cancer risk factors never develop it, while most women with breast cancer have no apparent risk factors.

Significantly higher risk

A woman with a history of cancer in one breast has a 3- to 4-fold increased risk of developing a new breast cancer, unrelated to the first one, in the other breast or in another part of the same breast. This is different than a recurrence of the previous breast cancer.

Moderately higher risk

Getting older. Your risk for breast cancer increases as you age. About 77% of women diagnosed with breast cancer each year are over age 50, and almost half are age 65 and older. Consider this: In women 40 to 49 years of age, there is a one in 68 risk of developing breast cancer. In the 50 to 59 age group, that risk increases to one in 37.

Direct family history. Having a mother, sister, or daughter ("first degree" relative) who has breast cancer puts you at higher risk for the disease. The risk is even greater if your relative developed breast cancer before menopause and had cancer in both breasts. Having one first-degree relative with breast cancer approximately doubles a woman's risk, and having two first-degree relatives increases her risk 5-fold. Having a male blood relative with breast cancer will also increase a woman's risk of the disease.