According to a recent article published in the Journal of the National Cancer Institute, estrogen receptor (ER) status of an initial breast cancer is strongly associated with ER status in subsequent breast cancer in the contralateral breast.
A significant portion of women with breast cancer has ER-positive breast cancer. ER-positive breast cancer refers to a type of breast cancer that is stimulated to grow from the naturally occurring female hormone estrogen. Women with ER-positive breast cancer often receive hormone therapy as a component of their therapeutic regimen. Hormone therapy, typically consisting of tamoxifen (Nolvadex®) or aromatase agents, inhibits the growth-stimulatory effects of estrogen on cancer cells. Women diagnosed with ER-positive breast cancer who are treated with tamoxifen also have a significant reduction in the risk of developing a breast cancer in the other (contralateral) breast.
Researchers from Pennsylvania and Ohio recently conducted a clinical study to evaluate the association between ER status with initial breast cancer and ER status in subsequent contralateral breast cancer. The study included data from 5,513 patients who were diagnosed with breast cancer and were involved in the National Surgical and Adjuvant Breast and Bowel Project trials B-18, B-22, and B-25. Of these patients, 176 developed contralateral breast cancer. All patients in these trials who were over the age of 50 years were treated with tamoxifen, regardless of ER status, and patients under the age of 50 did not receive tamoxifen. Among the group of patients who did not receive tamoxifen and developed a contralateral breast cancer, 89% of those with an ER-positive initial breast cancer had an ER-positive contralateral breast cancer, and 70% of those with an ER-negative initial breast cancer had an ER-negative contralateral breast cancer. Among the group of patients who did receive tamoxifen and developed a contralateral breast cancer, only 56% of those with an ER-positive initial breast cancer developed an ER-positive contralateral breast cancer, while 78% of those with an ER-negative initial breast cancer developed an ER-negative contralateral breast cancer.
The researchers concluded that an ER-positive status of an initial breast cancer is strongly associated with the same ER status in a contralateral breast cancer in patients who are not treated with tamoxifen and ER-negative status of an initial breast cancer is strongly associated with the same status in contralateral breast cancer. However, patients with an initial ER-positive breast cancer appear to have a reduced incidence of ER-positive contralateral breast cancer, indicating an overall reduction in contralateral breast cancer in patients with ER-positive breast cancer who are treated with tamoxifen. Clinical trials are currently underway to evaluate the use of aromatase agents in the prevention of breast cancer. It is important for patients with breast cancer to discuss the risks and benefits of tamoxifen or aromatase agents with their physician.
Reference: Swain S, Wilson J, Mamounas E, et al. Estrogen receptor status of primary breast cancer is predictive of estrogen receptor status of contralateral breast cancer. Journal of the National Cancer Institute. 2004; 96:516-523.