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Ki-67 Expression Appears to Identify Breast Cancer Patients Who Would Benefit From Letrozole Rather Than Tamoxifen: Presented at SABCS

By Ed Susman

SAN ANTONIO, TX -- December 17, 2007 -- High expression levels of Ki-67 protein in breast cancer tumors could be an indicator of which women will do better with adjuvant letrozole treatment than with tamoxifen.

"The value of Ki-67 as a marker of prognosis in postmenopausal women with estrogen-receptor-positive tumors is clear," said Giuseppe Viale, MD, Professor of Pathology and Laboratory Medicine, European Institute of Oncology, Milan, Italy. "A possible predictive role for response to adjuvant endocrine therapies is suggested."

Dr. Viale presented results from the Breast International Group (BIG) 1-98 study here on December 15 at the 30th Annual San Antonio Breast Cancer Symposium (SABCS).

The BIG 1-98 study randomized 4,922 women to receive the aromatase inhibitor letrozole or the selective estrogen-receptor modulator tamoxifen. The women were postmenopausal and had early-stage endocrine-responsive breast cancer. BIG 1-98 showed letrozole significantly improved disease-free survival compared with tamoxifen.

Researchers divided the women in the monotherapy arms of BIG 1-98 into those who had Ki-67 labeling index scores above or below 11%.

There were 2,685 women in the monotherapy arms who had material available for Ki-67 testing and who had positive estrogen-receptor status, Dr. Viale explained. He said that 1,252 women had Ki-67 labeling index scores higher than 11% and were designated as being high expressors of the protein.

After 5 years, doctors observed 122 events among patients with low Ki-67 index scores compared with 181 events in patients with high Ki-67 index scores (P <.0001).

The disease-free survival by treatment was not significantly different for women treated with letrozole or women with low Ki-67 scores if treated with tamoxifen, with survival between 90% and 93%. However, women with high Ki-67 scores who were treated with tamoxifen had a disease-free survival of 82% -- a difference that trended toward significance (P =.09).

The hazard of experiencing a disease-free survival event with letrozole was half the hazard with tamoxifen, Dr. Viale said (hazard ratio = 0.53; 95% confidence interval, 0.39-0.72).

The study was supported by Novartis.


[Presentation title: Value of Centrally-Assessed Ki-67 Labeling Index as a Marker of Prognosis and Predictor of Response to Adjuvant Endocrine Therapy in the BIG 1-98 Trial of Postmenopausal Women With Estrogen Receptor-Positive Breast Cancer. Abstract 64]

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