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.
Keywords: Breast cancer; Cancer registry; Chemotherapy; Gene expression profiling; Genomics.