How Family History Contributes to Breast Cancer Risk

by PJ Hamel Patient Expert

Does breast cancer "run in the family"? Inheriting BRCA1 or BRCA2 genes from either parent raises your risk of being diagnosed with breast cancer significantly. But how about a family history of breast cancer, without the BRCA genes? Find out how breast cancer in other family members increases your risk of being diagnosed - or doesn't.

Once you've been diagnosed with breast cancer, the impact of family history on your chance of getting breast cancer drops off your personal radar screen - you've already got it. Case closed.

But if you're cancer-free, and know of others in your family who've had cancer - how much is your risk of breast cancer increased?

Or, if you've just been diagnosed, is your daughter or mother at increased risk? How about cousins?

Does your dad's prostate cancer increase your breast cancer risk? How about the lung cancer that seems to have run through a cousins' family like wildfire? And your grandmother had breast cancer" didn't she?

A family's experience with cancer can be difficult to untangle. You may have never known about grandparents or great-grandparents struggling with cancer; children are usually sheltered from their elders' serious health issues. And, 50 years ago, cancer wasn't something people talked about; it was considered rather shameful, especially breast cancer.

The same is true of second-degree relatives and beyond (those not in your immediate family: parent, child, sibling). Unless you're a particularly close extended family, you may never know about a minor melanoma or treatable thyroid cancer in relatives you seldom see or connect with.

Luckily, when assessing your risk for breast cancer, you don't have to worry about any family history beyond that for breast cancer, and possibly ovarian cancer. As far as researchers have been able to determine, other cancers in your family don't increase your risk for breast cancer. So, your uncle's leukemia or your brother's sarcoma won't increase your breast cancer risk.

What kind of family history DOES increase your risk of being diagnosed with breast cancer?

If you have a first-degree family member with breast cancer (daughter, mother, sibling), your risk is a bit more than doubled: your relative risk is 2.1, in technical terms. The more first-degree relatives with breast cancer (and the younger they were diagnosed), the higher your personal risk.

But keep in mind, your risk is already fairly low. If you're 40 years old, your risk of developing breast cancer by your 50th birthday would normally be 1 in 70. With a first-degree relative, it's about 1 in 35; still great odds.

If you're younger, the odds are even lower; older, and they increase. If you're 70 years old, and your mother, a sister, or a daughter had breast cancer, chances are 1 in 13 you'll be diagnosed by your 80th birthday - higher, but still very much in your favor.

What about second-degree relatives - say, your aunt had breast cancer, or your cousin and your grandmother?

Depending on a number of factors, including how many second-degree relatives and their age at diagnosis, your risk is increased somewhat - but not as much as it is by a first-degree relative with breast cancer.

Now, what about those genetic mutations you've heard about - the BRCA1 and BRCA2 genes?

Many women, upon learning they have breast cancer, immediately want their genes tested, to see if other family members could be at risk. But such testing is almost always unwarranted.

Only a tiny percentage of the American population is at enough risk to undergo genetic screening. If you have breast cancer, your risk of carrying a mutated gene is only about 2.4%. If you don't have breast cancer, the risk drops to less than 1%. So keep these statistics in mind, if you're considering asking about genetic testing.

Still, there are certain women who should definitely consider screening for BRCA1 and BRCA2, even if they haven't been diagnosed with breast cancer. You're a good candidate for genetic testing if you have:

"¨"¨-A personal history of breast cancer diagnosed at age 40 or younger;

"¨-A personal history of bilateral breast cancer (cancer in both breasts), diagnosed at age 50 or younger;

"¨-A personal history of both breast and ovarian cancers;

"¨-Two or more first-degree relatives diagnosed with breast cancer before age 50;"¨

-Three or more first- or second-degree relatives diagnosed with breast cancer (any age);"¨

-A male relative with breast cancer;"¨

-A first- or second-degree relative with both breast and ovarian cancers;"¨

-A first-degree relative with bilateral breast cancer (cancer in both breasts);"¨

-Two or more first- or second-degree relatives with ovarian cancer;"¨

-A relative who tested positive for BRCA1 or BRCA2 ;

"¨-Ashkenazi (Eastern European) Jewish ancestry, with or without a family history of breast or ovarian cancer.

"¨"¨Some doctors narrow this down further to include being Ashkenazi Jewish with a first-degree relative with breast or ovarian cancer; or with two second-degree relatives, from the same side of the family, with breast or ovarian cancer.

For more information on genetic screening, read BRCA Genetic Testing: Yes or No?

Should you worry about a family history of breast cancer?

No, don't worry; it never helps. But an awareness of who in your family, if anyone, has had breast cancer (on either side, mom's or dad's) can help direct decisions around screening. It's easier to decide if that mammogram at age 40 is really necessary, once you know your personal odds.

PJ Hamel
Meet Our Writer
PJ Hamel

PJ Hamel is senior digital content editor and food writer at King Arthur Flour, and a James Beard award-winning author. A 16-year breast cancer survivor, her passion is helping women through this devastating disease. She manages a large and active online survivor support network based at her local hospital and shares her wisdom and experience with the greater community via