Twenty Years and Counting: Tamoxifen Benefit in Breast Cancer

Diana Kwon

May 11, 2022

A study presented at ESMO Breast Cancer 2022 documents a "significant long-term benefit" among women with breast cancer who were treated with tamoxifen.

The study was a secondary analysis of women with estrogen receptor (ER)-positive HER2-negative breast cancer who were treated between 1976 and 1996 in Sweden.

"Our findings suggest a significant long-term tamoxifen treatment benefit among patients with larger tumors, lymph node-negative tumors, PR-positive tumors, and Ki-67 low tumors," according to Huma Dar, a doctoral candidate at Karolinska Institute, Stockholm, who authored the study.

The analysis found that patients with tumor size T1c, grade 2, lymph node-negative, PR-positive, and Ki-67-low tumors significantly benefited from treatment with tamoxifen for 20 years. And, for patients with tumor size T2-3, benefited significantly after 10 years of treatment with tamoxifen.

It is known that breast cancer patients with ER-positive tumors have a greater risk of distant recurrence – cancer spreading to tissues and organs far from the original tumor site. The selective estrogen receptor modulator tamoxifen, when used as an adjuvant therapy, has been shown to reduce the risk of tumor recurrence and increase survival in patients with ER-positive breast cancer, but not all patients benefit from this therapy.

To examine the long-term benefit of tamoxifen, Dar and colleagues analyzed data from randomized clinical trials of tamoxifen that took place in Stockholm between 1976 and 1997. The study included 1,242 patients with ER-positive/HER2-negative breast cancer and included a 20-year follow-up. Researchers looked at the relationship between tumor characteristics – including size, grade, lymph node status, the presence of progesterone receptor (PR), and levels of Ki-67, a protein linked with cell proliferation – and patient outcomes.

In a related study published last year in JAMA Network Open, Dar and colleagues examined the long-term effects of tamoxifen in patients with low risk, postmenopausal, and lymph-node negative cancer. They found that patients with larger tumors, lower tumor grade and PR-positive tumors appeared to significantly benefit from tamoxifen treatment for up to 25 years. The team has since extended that work by looking at pre- and postmenopausal as well as low- and high-risk patients, Dar said.

"We believe that our findings together with other study findings are important to understand the lifetime risk for patients diagnosed with breast cancer," Dar said. "One potential clinical implication is related to tamoxifen benefit, which in our study we don't see for patients with the smallest tumors." She said that more studies are needed to confirm this result.

A limitation of this study is that clinical recommendations for disease management and treatment have changed since the initiation of the clinical trials. "The STO-trials were performed before aromatase inhibitors or ovarian function suppression became one of the recommended treatment options for ER-positive breast cancer, and when the duration of tamoxifen therapy was shorter than current recommendations," Dar said.

The study was funded by the Swedish Research Council, Swedish Research Council for Health, Working life and Welfare, the Gösta Milton Donation Fund, and Swedish Cancer Society. The authors had no relevant disclosures.

This article originally appeared on, part of the Medscape Professional Network.


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