Comparison of HER2 and Phospho-HER2 Expression between Biopsy and Resected Breast Cancer Specimens Using a Quantitative Assessment Method

BACKGROUND: HER2/Neu (ErbB-2) overexpression, which occurs in 15–20% of breast cancer cases, is associated with better response to treatment with the drug trastuzumab. PhosphoHER2 (pHER2) has been evaluated for prediction of response to trastuzumab. Both markers are heterogeneously detected and are potentially subject to loss as a consequence of delayed time to fixation. Here, we quantitatively assess both markers in core needle biopsies (CNBs) and matched tumor resections to assess concordance between the core and the resection and between HER2 and pHER2. METHODS: A selected retrospective collection of archival breast cancer cases yielded 67 cases with both core and resection specimens. Both HER2 and pTyr(1248)HER2 were analyzed by the AQUA® method of quantitative immunofluorescence on each specimen pair. RESULTS: Both HER2 immunoreactivity (P<0.0001) and pTyr(1248)HER2 immunoreactivity (P<0.0001) were lower in resections relative to CNB specimens. However, clinical implications of this change may not be evident since no case changed from 3+ (CNB) to negative (resection). Assessment of pTyr(1248)HER2 showed no direct correlation with HER2 in either CNB or resection specimens. CONCLUSIONS: The data suggest that measurement of both HER2 and phospho- Tyr(1248)HER2, in formalin-fixed tissue by immunological methods is significantly affected by pre-analytic variables. The current study warrants the adequate handling of resected specimens for the reproducible evaluation of HER2 and pHER2. The level of pTyr(1248)HER2, was not correlated to total HER2 protein. Further studies are required to determine the significance of these observations with respect to response to HER2 directed therapies.