Researchers at Karolinska Institutet in Sweden have discovered that the risk of death from breast cancer is twice as high for patients with high heterogeneity of the estrogen receptor within the same tumor as compared to patients with low heterogeneity. The study, which is published in the Journal of the National Cancer Institute, also shows that the higher risk of death over a span of 25 years is independent of other known tumor markers and also holds true for Luminal A breast cancer, a subtype with a generally good prognosis.
The most common form of breast cancer is estrogen-receptor-positive, so called hormone-sensitive breast cancer. This means that the tumor needs the female hormone estrogen to grow. Women who develop this kind of breast cancer have a remaining long-term risk of dying of the disease. It is also known that the estrogen receptor can change when a breast cancer tumor spreads, which affects survival. Why this is the case, however, is not known, but a possible explanation is that there are tumor cells in one and the same tumor with varying degrees of expression of the estrogen receptor. This is known as intra-tumor heterogeneity.
In the present study, Swedish and American researchers sought to discover if breast cancer patients with high heterogeneity of the estrogen receptor in their breast cancer tumor have a higher long-term risk of dying. To this end, they studied the fates of 593 patients in a clinical study, who had been either treated with tamoxifen or not treated with systemic therapy after surgery. All women had been diagnosed with post-menopausal estrogen-receptor-positive breast cancer between 1976 and 1990.
"Our study shows that patients with high intra-tumor heterogeneity of the estrogen receptor were twice as likely to die up to 25 years after their diagnoses as compared to patients with low heterogeneity," says Linda Lindström, researcher at the Department of Biosciences and Nutrition, Karolinska Institutet. "And this was independent of whether or not they'd received tamoxifen and of other known tumor markers."
The researchers also discovered that the greater risk of death for patients with high intra-tumor heterogeneity also applied to patients with Luminal A breast cancer, a subtype of estrogen-receptor-positive breast cancer that is considered to have a good prognosis.
"Patients with Luminal A breast cancer and high intra-tumor heterogeneity of the estrogen receptor were also twice as likely to die from the disease," continues Lindström. "This is interesting given that patients with Luminal A breast cancer subtype are generally thought to have a good prognosis. We believe that if validated, these new findings should be useable within the near future."
Journal of the National Cancer Institute, online edition, January 19, 2018
Karolinska Institutet (http://www.ki.se)