We have known for a long time that women who get breast cancer in one breast have an increased risk of getting a second primary tumor in the other breast. This knowledge has resulted in a significant rise in prophylactic mastectomies, as women aim to prevent cancer from occurring in the other breast. The real question is whether the contralateral breast cancer risk is the same for everyone. 

We know, for instance, that women with lobular cancers have about a 20% lifetime risk of getting cancer in the other breast; the risk for women with ductal cancers is 15%, or 1% per year. And, of course, women who carry the mutation for breast cancer (BRCA 1) have an increased risk of getting a tumor in the other breast. But can we parse the risk further so that we actually know which women would benefit from more surveillance or even prophylactic surgery?

A group from Northern California made a first step to figure this out.  They looked at all the women who had been diagnosed with breast cancer in the Surveillance, Epidemiology and End Results program (SEER database) and divided them into two groups: those with hormone positive tumors and those with hormone negative tumors. They also had information on ethnicity, age, and whether or not a second tumor developed in the other breast. Unfortunately they did not have information on whether the women in the SEER database were mutation carriers, HER2/neu positive, or took hormone therapy, so the result of this study is the big picture without a lot of nuance. Nonetheless the data are interesting and not surprising. 

First of all, the younger women (those under 30) have a higher risk of a second cancer. This is expected since they are more likely to be mutation carriers and have a lot of life years ahead of them. The women who had estrogen negative tumors had a higher risk of second tumors compared to those with estrogen positive tumors.  There are several explanations for this. One is that the women with estrogen positive tumors are usually older and often had taken postmenopausal hormone therapy. When diagnosed, they usually stop the hormones and start on Tamoxifen or an aromatase inhibitor, both of which decrease the risk of second cancers.

On the other hand, the estrogen negative women are usually younger (more time to get a second tumor) and more likely to have hereditary cancer and, therefore, to have both breasts at risk. Although women with BRCA mutations can reduce their risk by having their ovaries removed, it is not clear that this strategy would work for women who are not mutation carriers. This also feeds right into one of my current pet hypothesis: there are probably two different big groups of breast cancer that should be thought of as separate diseases. (I will blog more on that later).

So should you be scared? Looking at everyone across the whole period of follow up, the risk of a second hormone negative tumor is five times higher than the risk of a second hormone positive one. But these are not huge numbers. (A hormone negative tumor creates a risk of 24/10,000 person years versus hormone positive tumors, which carry a risk of 20 per 10,000 person years.) More interesting are the young women, where risks for a second hormone negative tumor were high in women initially diagnosed under 50 (34/10,000 person years); and highest in women initially diagnosed under 30 (36/10,000 person years).

The risk of second tumors also varies by ethnicity. Non-Hispanic blacks, Hispanics, and non-Hispanic Asian or Pacific Islander patients had a slightly greater risk of second cancers than non-Hispanic whites. Since these ethnic groups also have more estrogen negative tumors at a younger age, the findings make sense.  

Whether these levels of risk are enough for you to consider preventative surgery is obviously an individual choice. In the young women (diagnosed with hormone negative tumors under 30 or even 50) it might suggest yearly MRI or other screenings, although this has not been studied. Most importantly it tells us that we need to figure out the causes of breast cancer. Treating a young woman with chemotherapy, surgery, and radiation without figuring out what caused the cancer in the first place is putting her at risk of having it happen again. 

Join the Army of Women (www.armyofwomen.org) and help us sort this out once and for all!