Discrepancies in three commercial prognostic breast cancer assays used in adjuvant chemotherapy decisions.

Abstract

84 Background: OT (Oncotype DX), MS (Mammostrat) and MP (Mammaprint) are three prognostic measures of breast cancer recurrence risk. All three were retrospectively validated in large patient cohorts and are now used when deciding on risk-reducing adjuvant chemotherapy. Our objective was to directly compare these three assays and their potential for differential effects on adjuvant chemotherapy decision making. Methods: We have previously reported that OT reduces adjuvant chemotherapy utilization, whereas MS did not exhibit this same net tendency in identical patients. In this study, we performed MP assays in 31 ER+ N0 breast cancer patients for which we already had OT and MS results. Decision analysis was applied to determine changes in management that would be most likely depending on which assay was used to guide decision making. Results: Our decision analysis demonstrated that in a substantial proportion of breast cancer patients, each of the three assays led to changes in adjuvant treatment decisions compared with what would have been chosen based upon conventional criteria alone. OT changed the decision in 55% of patients, and MS and MP would have changed those decisions in 45% and 65% of patients, respectively. In two-by-two paired analyses, treatment decisions would have differed in 61% of cases for OT versus MS; 29% for OT versus MP and 38% for MS versus MP. OT had the greatest tendency to eliminate adjuvant chemotherapy use (in 55% of patients versus MS and in 22% of patients versus MP), whereas MS had the greatest tendency to increase chemotherapy use (in 55% of patients versus OT and 35% versus MP). Conclusions: In this study of 31ER+ N0 breast cancer patients, three commercially available prognostic assays (OT, MS and MP) often yielded discordant risk category results. Our decision analysis suggests that these discordant results may frequently lead to different chemotherapy choices based upon which assay had been selected to guide decision making.