Breast cancer testing strategies and the utilization of targeted therapies: Data from the real world

e17518 Background: HER2 testing and the use of trastuzumab is considered a prototype for the translation of a genomic therapy, yet almost nothing is known about use in practice. Uncertainties about the performance of the two types of HER2 tests, immunohistochemistry (IHC) and fluorescence-in-situ-hybridization (FISH) have led to debate about how best to identify women who are most likely to benefit from this costly treatment. Similarly, little is known about the use of gene expression profiling (GEP - e.g., OncotypeDx), which offers the possibility of better recurrence estimation to tailor the use of adjuvant chemotherapy. Methods: Cross-sectional record review of women, 36–64 years, with a new diagnosis of breast cancer in 2006–2007, identified using claims from a large, national health plan (n = 392 to date). Results: Almost all women had a HER2 test (97.7%): 56.2% had IHC alone, 17.4% had FISH alone, and 24.0% had both (2.4% had documentation of a test but not test type). Data for women with both IHC and FISH is shown below. Using the maximum of all available results, 24.9% were HER2-positive, 11.1% intermediate, and 63.9% HER2-negative. Only 55.2% of HER2-positive women received trastuzumab, compared to 16.7% of women with an intermediate score, and no HER2-negative women. The majority of women (85.7%) did not have GEP. Among women with GEP, 58.9% indicated low recurrence risk, 21.4% medium risk, and 5.4% high risk. Adjuvant chemotherapy was received by 27.3%, 91.7%, and 100% respectively (p < 0.001). Conclusions: HER2 tests, primarily IHC, are widely used. There are discrepancies in classification of HER2 status based on IHC vs. FISH. We did not find evidence of overuse of trastuzumab by women who were HER2-negative. Further work should clarify whether the lack of trastuzumab for HER2-positive women is clinically appropriate. We found modest adoption of GEP, and GEP score was associated with the use of adjuvant chemotherapy. [Table: see text] No significant financial relationships to disclose.