In the Breast International Group (BIG) and North Central Cancer Treatment Group (NCCTG) co-led phase III adjuvant breast cancer trial, ALTTO (Adjuvant Lapatinib and/or Trastuzumab Treatment Optimisation), two central laboratories, the European Institute of Oncology (IEO; Milan, Italy) and Mayo Clinic (Rochester, MN), are responsible for confirming the human epidermal growth factor receptor-2 (HER2), estrogen receptor α(ER), and progesterone receptor status of the primary breast tumors for the Rest of World (excluding China, which conducts a separate central review) and North American patients, respectively, prior to patient study entry. As of December 2009, discordance in HER2 and ER testing between local and central laboratories was observed by both central laboratories. For IEO, 14.5% of 8,037 HER2 cases locally positive [by either immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH)] were not able to be confirmed as centrally positive; whereas for Mayo, 5.8% of 412 HER2 cases locally positive were not able to be confirmed as centrally positive (Table 1). Central and local IHC ER discordance was 12.1% and 11.7% for 9,021 IEO screened cases and 419 Mayo screened cases, respectively (Table 2). In particular, IEO observed more false-positive (locally positive/centrally negative) HER2 findings than Mayo and Mayo observed more false-positive ER findings than IEO. Purpose: Motivated by the above findings, we launched a ring study to assess whether the central lab results of a subset of local/central discordant ALTTO cases could be confirmed in the other central lab. Methods: IEO and Mayo exchanged and retested a subset of FFPE breast tumors collected in ALTTO. IEO sent 20 HER2 false-positive, 5 ER false-positive, and 5 ER false-negative (locally negative/centrally positive) ALTTO breast tumors to Mayo. Mayo sent 5 HER2 false-positive, 20 ER false-positive, and 5 ER false-negative ALTTO breast tumors to IEO. IEO and Mayo performed IHC for ER according to their own methodology: DAKO cocktail of ER 1D5 and 2.123 monoclonal antibodies and monoclonal ER 1D5 antibody, respectively. The two laboratories performed IHC for HER2 according to the HercepTest® manufacturers’ instructions (Dako, Carpenteria, CA) and FISH for HER2 using the PathVysion HER2 DNA probe kit and the HER2/centromere 17 probe mixture (Abbott Molecular, Des Plaines, IL). Results: IEO and Mayo confirmed the central HER2-negative result in 100% of 25 cases. Analyses of ER are ongoing and ER results will be presented. Conclusions: In this subset of patients, enrollment ineligibility did not change when HER2 testing was performed by either IEO or Mayo Clinic central laboratories.

Table 1. HER2 Local/Central Lab Results

Table 2. ER Local/Central Lab Results

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-10-36.