The incidence of advanced breast cancer among women aged 25 to 39 years increased by an average of 2.07% per year from 1976 to 2009 and the trend seems likely to continue, according to an analysis of data for 936,497 women diagnosed with malignant breast cancer. The small but statistically significant increase should serve to alert young women and their physicians that “breast cancer can and does occur” in younger women and that changes in the breast warrant follow-up, the study’s lead author, Rebecca H. Johnson, MD, said in an interview with The ASCO Post. Dr. Johnson is Medical Director of the Adolescent and Young Adult Oncology Program at Seattle Children’s Hospital and Assistant Professor at the University of Washington in Seattle.
Data from the U.S. Surveillance, Epidemiology, and End Results (SEER) program showed “the incidence of breast cancer with distant involvement at diagnosis increased in 25- to 39-year-old women from 1.53 (95% confidence interval [CI] = 1.01–2.21) per 100,000 in 1976 to 2.90 (95% CI = 2.31–3.59) per 100,000 in 2009. This is an absolute difference of 1.37 per 100,000, representing an average compounded increase of 2.07% per year (95% CI = 1.57%–2.58%; P < .001) over the 34-year interval,” according to the study report published in the Journal of the American Medical Association.1
SEER definitions of extent of disease at diagnosis refer to distant disease as involving remote metastases, for example, to the bone, brain, or lung. Similar increases in incidence were not found for localized disease (defined by SEER as confined to the breast) or regional disease (defined as contiguous and adjacent organ spread, such as to lymph nodes or the chest wall), or for age groups other than those 25 to 39.
Personal Experience with Breast Cancer
Dr. Johnson has firsthand knowledge about breast cancer in young women. She discovered a lump in her breast and was diagnosed with breast cancer when she was 27. “It was a 2-cm tumor, stage I, with negative lymph nodes, 0 out of 26,” she said. “I had a mastectomy and then chemotherapy.”
She was a medical resident back then and in reviewing the medical literature found much of it focused on breast cancer as a disease of older women. After being diagnosed, however, “I kept hearing from friends, and friends of friends, and distant relatives about more than a dozen cases of breast cancer in young women,” she said. Two of about 15 other people in a Houston book group that she belonged to while completing fellowships in clinical genetics and pediatric oncology were also diagnosed with breast cancer before age 35. (One was interviewed by National Public Radio as part of the coverage of the study.2)
Her personal experience with breast cancer and meeting other young women with breast cancer led her to question whether breast cancer among younger women “is a significant health problem that has always been here, but that we just didn’t talk about. Or is there really some sort of an increase?”
She and her colleague and coauthor, Archie Bleyer, MD, of St. Charles Health System, Central Oregon, and Oregon Health and Science University, Portland, started tackling these questions for a research task force on breast cancer organized by the LIVESTRONG Young Adults Alliance to “identify what was different about the cancers of teens and young adults,” Dr. Johnson explained. “I had a personal interest in breast cancer, even though I don’t see patients with breast cancer,” and Dr. Bleyer had been involved in many SEER data analyses, including one that found breast cancer is the most common cancer of 15- to 39-year-old women, comprising about 25% of all cancers in that age group.
Those data were used to answer the question, If you are a woman and you are under 40, what is your chance of getting breast cancer? The results, published in Seminars in Oncology,3 “showed that your chances of getting breast cancer as a woman in the United States by the time you or are 40, is 1 in 173,” Dr. Johnson noted. “So I thought that most women won’t get breast cancer when they are under 40, but most women will know someone who does.”
Tripling of Incidence
“The next question, which led to this study that we just published in JAMA, was: What has been the change in incidence over time, and is that actually increasing or is it static? When you look at the whole population by age since the mid-1970s, when the SEER database really got up and running, you don’t see a change in the rate of young adult breast cancer. But when we broke it down by stage at diagnosis, that was when we identified the increase in metastatic breast cancer.”
The 2.07% average compounded increase per year in the incidence of advanced cancer among younger women was somewhat surprising, Dr. Johnson admitted. It was probably not apparent earlier, she added, because the actual number of cases was small compared to the large number of older women with breast cancer and young women with earlier-stage breast cancer.
“If you project out to the population, it translates into an increase from about 275 or so metastatic breast cancers in younger women per year in the mid-1970s to about 850 in 2008/2009,” she explained. “So, essentially, it is a tripling of the incidence. On a population basis, it is a small change. But if a pediatric cancer had tripled from 275 to 850 cases, we would certainly worry about it.”
Reasons Remain Unknown
The reasons for the rise in metastatic breast cancer among younger women remain unknown, although some media reports included comments speculating about possible causes. Others expressed skepticism about an increase.
Despite “quite an extensive literature review looking at risk factors and their temporal trends over the past 35 years to see if there was one single thing that really correlated with this increase, I didn’t find anything that by itself was a potential explanation,” Dr. Johnson said. While the rise in obesity has raised health concerns, “in terms of breast cancer incidence, obesity or being overweight is actually protective against getting breast cancer as a young adult. That has been shown in really large prospective studies,” she noted.
“However, being obese is a risk factor for dying from breast cancer,” she continued. In addition, “some smaller studies suggest that if you take several risk factors at a time, like obesity, sedentary lifestyle, and high caloric intake, for example, the three of those together do predict an increased risk of premenopausal breast cancer,” Dr. Johnson said.
“Whatever the causes—and likely there are more than one—the evidence we observed for the increasing incidence of advanced breast cancer in young women will require corroboration and may be best confirmed by data from other countries,” the authors concluded. Because the SEER database includes such a large sample of patients with breast cancer from the United States, and the findings were significant, “we think that the best thing to do would be to look at other very large samples—in Canada, in Australia, in Europe—in order to get enough patients to confirm the results,” Dr. Johnson explained.
Other experts commenting to the media also called for confirmation of the results, including ASCO President Sandra M. Swain, MD, FACP, Medical Director of the Washington Cancer Institute at the MedStar Washington Hospital Center in Washington, DC, who was interviewed by NBC News.4 ■
Disclosure:Drs. Johnson and Bleyer reported no potential conflicts of interest.
References
1. Johnson RH, Chien FL, Bleyer A: Incidence of breast cancer with distant involvement among women in the United States, 1976 to 2009. JAMA 309:800-805, 2013.
2. Knox R: Younger women have rising rate of advanced breast cancer, study says. National Public Radio, February 27, 2013. Available at npr.org/blogs/health.
3. Anders CK, Johnson R, Litton J, et al: Breast cancer before age 40 years. Semin Oncol 36:237-249, 2009.
4. Fox M: Aggressive breast cancer in more young women, study finds. NBC News Vitals, February 26, 2013. Available at vitals.nbcnews.com.
