High levels of the Ki-67 protein are associated with poor prognosis in early breast cancer patients, but it may not able to predict which patients will benefit from additional chemotherapy.
The percentage of proliferating cells in a tumor is a predictor of breast cancer prognosis. The level of Ki-67 expression is sometimes used as a measure of cell proliferation. Some studies have suggested that breast tumors with a high percentage of cells expressing Ki-67 are more responsive to chemotherapy.
Giuseppe Viale, M.D., of the University of Milan in Italy and colleagues at the International Breast Cancer Study Group conducted research to determine whether Ki-67 expression could predict responsiveness to chemotherapy given after breast cancer surgery. They assessed Ki-67 expression in tumor samples taken from patients in two randomized clinical trials that compared endocrine therapy given after chemotherapy with endocrine therapy alone.
The researchers found that Ki-67 expression did not predict which women would benefit from chemotherapy prior to endocrine therapy. However, having a high percentage of cells expressing Ki-67 was associated with poorer disease-free survival.
"In this study, Ki-67 [expression] was a prognostic factor, not a predictive factor," the authors write.
In an accompanying editorial, Matthew Ellis, Ph.D., of Washington University in St. Louis notes that these results support the position of the American Society of Clinical Oncology Tumor Markers Expert Panel that Ki-67 should not be used the make decisions about chemotherapy.
"Biomarker studies with negative results can be just as important to publish as those with positive results...because clinging to a long-favored but incorrect hypothesis in the face of negative evidence impedes scientific and clinical progress," Ellis writes.
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