Hormonal Therapy Has A Long Term Effect In Breast Cancer

Researchers at Karolinska Institutet in Sweden have investigated the long-term effect of hormonal therapy in women with the most common types of hormone-sensitive breast cancer. The results, presented in the journal JAMA Oncology, show 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.

Estrogen receptor-positive (hormone sensitive) breast cancer is the most common form of breast cancer; also 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; so of distant metastatic spread of the disease and dying from breast cancer. There is however insufficient knowledge of how biological factors in the tumor and hormonal therapy affect this long-term risk.

Effect of hormonal therapy

Researchers at Karolinska Institutet have now investigated the long-term effect of hormonal therapy in women; so with the two most common types of estrogen receptor-positive breast cancer. The researchers analyzed long term data with follow-up for at least 20 years for patients; so in the Stockholm Tamoxifen trial (STO-3) randomised to receive either tamoxifen treatment or no hormonal therapy. In summary, 336 women were diagnosed with so-called Luminal A breast cancer subtype and 126 women with Luminal B subtype.

The results show that patients with Luminal A breast cancer had a relatively small; but prolonged risk increase for metastatic cancer, and that tamoxifen treatment significantly reduced this risk for as long as 15 years after diagnosis. Patients with Luminal B subtype were at high risk; so for metastatic breast cancer during the first five years after diagnosis. In these patients, tamoxifen treatment led to a significantly reduce risk during the first five years; but after that the protective effect of hormonal therapy decreased.

The aggressive tumours

“Our conclusion is 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,” says Dr. Linda Lindstrom, a research group leader at Karolinska Institutet’s Department of Biosciences and Nutrition, who coordinated the study. “Patients with Luminal B breast cancer should also be offered hormonal therapy; also our results show a reduced risk of metastatic disease; hence during the first years when the risk is the highest for these patients.

They will now proceed to investigate the long-term benefits of hormonal therapy in patients with Luminal A and Luminal B sub type who have diagnose with larger and aggressive tumours with spread to the lymph nodes.”The study was funded by the Swedish Research Council, Forte, the Gosta Milton Donation Foundation; the California Breast Cancer Research Program Award, Iris, Stig and Gerry Castenbäck’s Foundation for Cancer Research. Co-author Laura van’t Veer holds a patent for “Mammaprint 70-gene risk signature” and is co-founder, shareholder and part-time employee at Agendia.