In a new study, researchers have examined the long-term effect of hormonal therapy in women with the most common types of hormone-sensitive breast cancer.
They found that the treatment has a protective effect against distant metastatic cancer for both so-called Luminal A and Luminal B breast cancer subtypes and a long-term effect for women diagnosed with Luminal A cancer.
The research was conducted by a team at Karolinska Institutet in Sweden.
Estrogen receptor-positive (hormone-sensitive) breast cancer is the most common form of breast cancer.
It means that the tumor grows in response to the female hormone estrogen.
Women who develop this form of breast cancer have a long-term risk of distant metastatic spread of the disease and dying from breast cancer.
However, there is insufficient knowledge of how biological factors in the tumor and hormonal therapy affect this long-term risk.
In the study, the team tested the long-term effect of hormonal therapy in women with the two most common types of estrogen receptor-positive breast cancer.
They analyzed long-term data with follow-up for at least 20 years for patients who received either tamoxifen treatment or no hormonal therapy.
A total of 336 women were diagnosed with so-called Luminal A breast cancer subtype and 126 women with Luminal B subtype.
The team found patients with Luminal A breast cancer had a small but prolonged risk increase for metastatic cancer, and that tamoxifen treatment strongly reduced this risk for as long as 15 years after diagnosis.
In addition, people with Luminal B subtype were at high risk for metastatic breast cancer during the first five years after diagnosis.
In these patients, tamoxifen treatment led to a strongly reduced risk during the first five years, but after that, the protective effect of hormonal therapy decreased.
The team concludes that tamoxifen treatment is beneficial for both groups of patients, but that it has a long-term protective effect for patients with Luminal A breast cancer.
One author of the study is Dr. Linda Lindström, a research group leader at Karolinska Institutet’s Department of Biosciences and Nutrition.
The study is published in the journal JAMA Oncology.
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