We have known for a long time that women who get breast cancer in one breast have a higher risk of getting a second one in the other breast. We refer to this as a â€œcontralateral second primary breast cancer.â€ This knowledge has resulted in a significant increase in prophylactic mastectomies. The real question is whether the risk is the same for everyone. We know that women who have had a lobular cancer have a lifetime risk of developing a second cancer in the opposite breast of about 20%. (This means there is a 20% chance they will develop a second cancer in the opposite breast before they die.) For women who have had a ductal cancer, the lifetime risk is about 15%, or 1% per year. And women who have a genetic mutation that increases breast cancer riskâ€”BRCA1 or BRCA2â€”are at very high risk of developing cancer in the other breast. But can we parse the risk even further, so that we actually know which women would benefit from more surveillance or from prophylactic surgery?
A Northern California research group has taken the first step in trying to figure this out, and their findings were published July 9 in the Journal of the National Cancer Institute. The investigators used the Surveillance Epidemiology and End Results (SEER) database to identify 4,927 women who had been diagnosed with a first breast cancer between January 1992 and December 2004 in. (SEER collects and publishes cancer incidence and survival data from population-based cancer registries.) Then, they divided the women into two groups: those with hormone-positive tumors (ER/PR+) and those with hormone-negative tumors (ER/PR-). Then they looked at the womenâ€™s age, ethnicity, and whether they had developed a second tumor in the other breast. (Unfortunately, they did not have information about whether the women carried a BRCA1 or 2 genetic mutation, were Her2-positive, or had taken tamoxifen or an aromatase inhibitor as part of their cancer treatment.) This means we only get a big picture result, without a lot of nuances. Even so, the data are interestingâ€”and not surprising.
First, all the women who were 30 and under had a higher risk of a developing a cancer in the opposite breast. This would be expected, since they are more likely to be mutation carriers and to have a long life ahead of themâ€”and more years alive means more years in which to get a second tumor.
They also found that women who had ER-negative tumors had a higher risk of developing a tumor in the opposite breast than did women with ER-positive tumors. There are several explanations for this. that the first is that the women with hormone-positive tumors are usually older and often had taken postmenopausal hormone therapy. When diagnosed with breast cancer, they usually stop the hormones and start on tamoxifen or an aromatase inhibitor, both of which decrease the risk of a second cancer in the opposite breast. The second is that the women with hormone-negative tumors are usually younger (which means they have 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 feeds right into one of my current pet hypotheses: 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? The study showed that women whose first breast tumors were hormone-positive were at greater risk than the general population of developing a second tumor, but the risk is not that high. The researchers saw 13 more cases per year in this group of women than they would have expected to see if they had followed 10,000 women who had not had breast cancer. Women who had a hormone-negative tumor were more likely than those who had a hormone-positive tumor to develop a second cancer, and it was more likely to be another hormone-negative tumor. The researchers saw 20 more cases of hormone-positive tumors and 24 more cases of hormone-negative tumors per year than they would have expected to see if they were looking at a group of 10,000 women who had not had breast cancer.
More interesting are the young women where risk for a second hormone-negative tumor were high if they had been diagnosed under 50 (34/10,000 person years); and even higher if they had been diagnosed under 30 (77/10,000 person years). The risk of second tumors also varied by ethnicity, with non-Hispanic blacks, Hispanics, and non-Hispanic Asian or Pacific Islander patients having a slight greater risk of second cancers than non-Hispanic whites. This makes sense, since these ethnic groups also had more hormone-negative tumors and were more likely to develop them at a younger age.
Whether these levels of risk are enough for you to consider preventative surgery (prophylactic mastectomy) is obviously an individual choice. For the women who were diagnosed with hormone-negative tumors under age 30 or even under age 50 it might suggest that they would benefit from yearly MRI or other screening, but 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 and help us sort this out once and for all!