Abstract PD10-02: Round-Robin Review of HER2 Testing in the Context of Adjuvant Therapy for Breast Cancer (NCCTG N9831/BCIRG006/BCIRG005)

Abstract

Abstract Identification of HER2 as an important cellular marker in the biology and treatment of breast cancer has highlighted the importance of reliable testing methodology. Controversy exists regarding type of test, reliability, definition of positivity, and which test may best predict for patient (pt) efficacy to anti-HER2 therapies. Purpose: To determine the concordance between HER2 results by 3 central laboratories, impact of round-robin adjudication of discordant cases, and heterogeneity in HER2 results using specimens from 3 adjuvant trials where HER2 testing was performed by local and central laboratories for enrollment. Methods: We performed a blinded round-robin exchange of randomly sampled, HER2-normal (IHC-& FISH-) and HER2-positive breast tumors among 3 central laboratories (NCCTG, BCIRG and NSABP) for confirmatory HER2 testing. The 3 laboratories performed immunohistochemistry (IHC) for HER2 using the HercepTest kit (Dako, Carpenteria, CA) and fluorescence in situ hybridization (FISH) for HER2 using the PathVysion HER2 DNA probe kit/HER2/CEN17 probe mixture (Abbott Molecular, Des Plaines, IL) on 389 tumor specimens obtained from N9831/BCIRG006 (37 IHC+/FISH+, 33 IHC+/FISH-, 36 IHC-/FISH+, 62 IHC-& FISH-) and BCIRG005 (96 IHC-& FISH-); 123 cases had ≥2 blocks examined from the same pt. HER2 positivity was defined according to FDA-approved guidelines used in the clinical trials (IHC+: 3+ complete membrane staining in >10% cells; FISH+: HER2/CEN17 ratio ≥2.0). The HER2 status (IHC: 3+ vs 0-2+; FISH: amplified vs not) for each block was independently determined at each site; discordant IHC and FISH cases were adjudicated at a face-to-face meeting. Results: Independent reads were concordant across pathologists in IHC status in 351/381 (92%) cases and in FISH status in 343/373 (92%) cases. Upon adjudication, a consensus was reached on 16 and 18 of the discordant IHC and FISH cases, respectively. Among 96 BCIRG005 cases, IHC-and FISH-were confirmed in the primary block in all 96 cases. Among 59 evaluable N9831 HER2-normal cases, IHC-and FISH-were confirmed in the primary block in 57 (97%) cases (but another block tested HER2+ for 4 cases). Among 102 N9831/BCIRG006 HER2+ cases, HER2 positivity was confirmed in the primary block in 73 (72%) cases. Among 118 cases with IHC results for > 1 block, the adjudicated IHC result agreed across blocks in 106 (90%) cases. Among 113 cases with FISH results for >1 block, the adjudicated FISH result agreed in 107 (95%) cases. Among 53 N9831 HER2-normal cases adjudicated as IHC-& FISH-(although they all had a previous local HER2+ test), there was significant improvement in disease-free survival associated with trastuzumab given concurrently with paclitaxel after doxorubicin and cyclophosphamide compared to chemotherapy alone (HR=0.31, 95% CI 0.11-0.91; A 23 pts, 10 events; C 30 pts, 5 events). Conclusions: Excellent agreement (96%) was observed among the pathologists at adjudication, suggesting that standardized methods improve assay proficiency. HER2 heterogeneity across blocks was observed more at the protein than at the gene level. In the small subset of N9831 pts adjudicated as HER2-normal trastuzumab benefit was observed. This work was supported by NCI and Genentech. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD10-02.