The study reviewed here found that certain risk factors for breast cancer:
affect the risk of specific types of breast cancer in different ways.
The researchers analyzed the records of more than 2,500 women in two studies:
Hormone-receptor-positive, HER2-negative breast cancer (luminal A) is the most common type of breast cancer and tends to have a better prognosis than the other three types studied. Women diagnosed with hormone-receptor-positive, HER2-negative breast cancer are more likely to drink alcohol, use HRT, and be older compared to women diagnosed with the other types.
Hormone-receptor-positive, HER2-positive breast cancer (luminal B) tends to have a worse prognosis than hormone-receptor-positive, HER2-negative breast cancer but a better prognosis than the other two types. Women diagnosed with hormone-receptor-positive, HER2-positive breast cancer are likely to be younger, but less likely to drink alcohol or use HRT compared to women diagnosed with the other types.
Hormone-receptor-negative, HER2-negative breast cancer (triple-negative) tends to have a worse prognosis than the other types studied. Women diagnosed with triple-negative breast cancer are more likely to be younger, overweight, and African American compared to women diagnosed with the other types.
Hormone-receptor-negative, HER2-positive breast cancer (HER2 over-expressing) tends to have a worse prognosis than breast cancer that is hormone-receptor-positive. Women diagnosed with hormone-receptor-negative, HER2-positive breast cancer are likely to be younger and Hispanic or Asian, and less likely to use HRT compared to women diagnosed with the other types.
Understanding the ways specific risk factors can affect the risk of different types of breast cancer may help create programs targeted at specific groups of women at highest risk. For example, the results of this study suggest that a good way to lower the risk of triple-negative breast cancer would be to focus on young, overweight African American women because those three factors are linked to a higher risk of triple-negative breast cancer.
Visit the Breastcancer.org Lower Your Risk section to learn more about breast cancer risk and steps you can take to make sure your risk is as low as it can be.
RIDGEWOOD, N.J., May 22 (MedPage Today) -- Risk factors for the development of invasive breast cancer vary depending on whether the tumor is luminal A, luminal B, triple negative, or Her2-overexpressing, a new study has found.
Women with the luminal B breast cancer subtype, for instance, were likely to be younger at diagnosis than those with luminal A (OR before age 50 of 1.83, 95% CI 1.32 to 2.55, P=0.0001), Marilyn L. Kwan, Ph.D., of Kaiser Permanente in Oakland, Calif., and colleagues reported online in Breast Cancer Research.
Luminal B patients also were less likely to use hormone replacement therapy (OR 0.66, 95% CI 0.46 to 0.94) and oral contraceptives (OR 0.73, 95% CI 0.55 to 0.96), or to consume alcohol (OR 0.74, 95% CI 0.56 to 0.98), the investigators found.
Luminal A tumors are estrogen receptor and/or progesterone receptor positive and human epidermal growth factor receptor 2 (Her2) negative. Luminal B tumors are estrogen receptor and/or progesterone receptor positive, as well as Her2 positive.
These two subtypes have been associated with improved prognoses compared with the subtypes referred to as Her2 overexpressing and "triple negative" (basal-like in 70% of cases).
Her2-overexpressing tumors are estrogen receptor and progesterone receptor negative but Her2 positive, and triple negative tumors, as the name implies, are negative for all three, but positive for cytokeratin 5/6 and/or epidermal growth factor receptor in the majority of cases.
Previous studies have examined associations between breast cancer risk factors, race, and hormone receptor status, but few studies have investigated the relationship between risk factors and molecular subtypes.
To address this, the researchers examined data from two large, prospective breast cancer survivorship studies, the Life After Cancer Epidemiology (LACE) Study and the Pathways Study.
LACE involved 2,280 women diagnosed with early-stage invasive breast cancer between 1997 and 2000, recruited primarily from the Kaiser Permanente Northern California Cancer Registry and the Utah Cancer Registry.
Patients were 18 to 70 years old, had completed treatment other than adjuvant hormonal therapy, and were free of recurrence.
The Pathways Study is an ongoing prospective cohort study that began recruiting in January 2006 and currently includes 2,212 women.
Patients in this study were at least 21 years old at the time of diagnosis, have primary invasive breast cancer of any stage, and no prior history of any cancer.
The current analysis includes all patients in LACE and the first 723 women in the Pathways Study whose cancers corresponded with those in LACE (stage I e 1 cm, II, or IIIA) and for whom molecular subtype data were available.
Demographically, the pool of cohorts was relatively heterogeneous.
Among the 2,544 cases of invasive breast cancers included in the study:
Compared with luminal A cases, triple negative cases tended to be younger, (OR before age 50 of 2.78, 95% CI 1.99 to 3.90, P</= 0.0001) and to be African-American, (OR 3.14, 95% CI 2.12 to 4.16).
Her2-overexpressing cases were more likely to be younger than luminal A cases (P=0.03) and less likely to use HRT (OR 0.49, 95% CI 0.26 to 0.79).
Women with the Her2-overexpressing subtype also were more likely to be Hispanic (OR 2.19, 95% CI 1.16 to 4.13) or Asian (OR 2.02, 95% CI 1.05 to 3.88).
Premenopausal women with the triple-negative subtype were more likely to be overweight (OR 1.82, 95% CI 1.03 to 3.24) or obese (OR 1.97, 95% CI 1.03 to 3.77).
Women with the triple-negative subtype and parity of three or more also were more likely to have not breastfed their children (OR 1.68, 95% CI 1.00 to 2.81).
The "significant heterogeneity of associations by tumor subtype . . . lend[s] further support to the growing evidence base that breast cancer is a heterogeneous disease defined by estrogen receptor, progesterone receptor, and Her2 expression with distinct etiologic pathways and prognoses," the researchers concluded.
They cited study limitations that include the small number of Her2-overexpressing tumors, the case-case comparison design, and the fact that the associations reported are all in reference to risk of having the luminal A subtype "and should not be extended to risk of having invasive breast cancer."
Triple negative cases could not be further classified as basal-like or unclassified due to absence of data on CK 5/6 and EGFR markers.
These findings suggest that "public health programs aimed towards achieving a healthy weight and promoting breastfeeding might reduce the number of poor prognostic triple negative tumors among all breast cancer cases, especially the high-risk African American group," they concluded.
The LACE Study was funded by the National Cancer Institute, the Utah Cancer Registry, and the State of Utah Department of Health.
The Pathways Study was funded by the National Cancer Institute, the Department of Defense, and the American Cancer Society.
The authors declared that they have no competing interests.
Primary source: Breast Cancer Research Source reference: Kwan M, et al "Epidemiology of breast cancer subtypes in two prospective cohort studies of breast cancer survivors" Breast Cancer Res 2009: 11:R31.
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