UC Davis

Purpose

To describe the utilization of gene expression profiling (GEP) among California breast cancer patients, identify predictors of use of GEP, and evaluate how utilization of GEP influenced treatment of early-stage breast cancer.

Methods

All women diagnosed with hormone-receptor-positive, node-negative breast cancer reported to the California Cancer Registry between January 2008 and December 2010 were linked to Oncotype DX (ODX) assay results.

Results

Overall, 26.7 % of 23,789 eligible patients underwent the assay during the study period. Women age 65 or older were much less likely than women under age 50 to be tested (15.1 vs. 41.4 %, p < 0.001). Black women were slightly less likely and Asian women were slightly more likely than non-Hispanic white women to undergo GEP with the ODX assay (22.2 and 28.9 vs. 26.9 %, respectively, p < 0.001). Patients residing in low SES census tracts had the lowest use of the test (8.9 %), with the proportion increasing with higher SES category. Women with Medicaid health insurance were less likely than other women to be tested (17.7 vs. 27.5 %, p < 0.001). Receipt of adjuvant chemotherapy (ACT) was associated with the ODX recurrence score, although only 63 % of patients whose recurrence scores indicated a high benefit received ACT. Of patients not tested, 15 % received ACT.

Conclusions

Nearly three-fourths of eligible breast cancer patients in California during the 3-year period 2008 through 2010 did not undergo GEP. As a result, it is likely that many women unnecessarily received ACT and suffered associated morbidity. In addition, some high-risk women who would have benefited most from ACT were not identified.