Metastatic Breast Cancer Risk Test Quick to Be Adopted into Clinical Practice

The 21-gene recurrence score assay to predict the risk of metastatic disease and the potential benefit of adjuvant chemotherapy for women with breast cancer, has been quickly integrated into clinical practice. Moreover, the test is generally being used in line with guidelines across the US and among different racial groups. These are the results of a study published  in JAMA Oncology.

Medicare approved the use of the Oncotype DX 21-gene recurrence score assay (Genomic Health, Inc.) in 2006 for early-stage, estrogen-receptor positive, and node-negative breast cancer within 6 months of diagnosis who are considering tamoxifen or aromatase inhibitor therapy, which may help gauge the risk of cancer spread in these patients. This is the first examination of the use of this test in a national patient sample. The test has been available commercially in the US since 2004.

Current guidelines--both those from the National Comprehensive Cancer Network (NCCN) and American Society of Clinical Oncology (ASCO)--recommend use of the test to identify those women who have a relatively low risk of developing advanced/metastatic disease, and who may opt out of adjuvant chemotherapy, and high-risk patients who may have the greatest benefit from chemotherapy.

Michaela A. Dinan, PhD, of the Duke Clinical Research Institute and Duke University School of Medicine, in Durham, NC, and colleagues used a Surveillance, Epidemiology, and End Results (SEER) and Medicare linked data from 2005 to 2009. A total of 5.2% of breast cancer patients analyzed had the test performed during this time period.

Of a total of 70,802 patient records examined, use of the 21-risk score assay increased from 1.1% in 2005 to 10.1% in 2009 (P < .001). The greatest amount of testing occurred in patients with NCCN–defined intermediate-risk disease, and those with estrogen-receptor positive, node-negative tumors greater than 1 cm in size.  Use of the 21-risk score assay was associated with younger age patients and those with less comorbidity, higher grade of disease, and a married status.

Among those patients younger than 70 years with intermediate-risk disease, testing rates increased from 7.7% in 2005 to 38.8% in 2009 (P < .001).

Rates of chemotherapy use were similar in 2005 (16.2%) and 2009 (15.9%). In just those patients with intermediate-risk breast cancer, the increase in chemotherapy use went from 8.2% in 2005 to 10% in 2009-not a statistically significant increase.

There was no difference in the proportion of black patients who received the test and those that did not (5.7% and 5.9%, respectively).

The proportion of estrogen-receptor positive tumors diagnosed increased from 70.7% to 77.6% between 2005 and 2009.

Because the SEER registry included only Medicare patients, the study population was restricted to those 65 years of age and older and included mostly non-white, high-poverty area patients. Whether these results apply to the general population of women across the US diagnosed with breast cancer is not clear. 

“Further study is warranted in patients with breast cancer who are not included in the SEER-Medicare database, particularly younger women for whom the factors affecting chemotherapy use and assay use may differ from those observed in our study,” noted the study authors.

In an accompanying commentary, Lisa Flaum, M.D., and William J. Gradishar, M.D., of the Northwestern University Feinberg School of Medicine, in Chicago note that although the utilization of this newer molecular test appeared to be appropriate, the no change in the rates of chemotherapy use among older, intermediate-risk patients is a different result than that of the large meta-analysis of nine studies that showed use of the test led to a change in the frequency of chemotherapy use (Hornberger, p. 58).

The lack of change in chemotherapy use in the current study “suggests either that the physicians have a bias about treating older patients with chemotherapy that the test did not change regardless of results, or that the test results were concordant with their pretest bias,” wrote the commentary authors.

A prospective study of the physician-patient decision based on the 21-risk score test results would go towards answering this question which is important, as many low-risk older women with breast cancer would rather not receive chemotherapy.