Quantitative HER2 levels and steroid receptor expression in primary breast cancers and in matched brain metastases.

Abstract

603 Background: Breast cancer patients with HER2-positive tumors are at high risk for brain metastases. In the current study we examined expression of ER, PR and HER2 in primary breast tumors and in matched brain metastases, as changes of their levels might reflect modes of escape from therapy. Methods: Fifty-three pairs of matched formalin-fixed paraffin-embedded samples from primary breast cancers and brain metastases were assayed for ER and PR status by immuno-histochemistry, whereas HER2 expression was quantified using the novel HERmark assay. Nuclear staining of ER and PR >10%, and relative fluorescence of HER2 >17.8/mm2 were considered as positive results. Results: HER2 levels in brain metastases were generally higher than in the primary tumors (p = 3e-6), with a median increase of 1.9-fold (range 0.08 to 199-fold). There were also substantial differences in ER and PR status between primary tumors and brain metastases. Loss of steroid receptor positivity in brain metastases was more frequent than its gain (ER: 46% vs. 26%; p = 0.16; PR: 57% vs. 23%; p = 0.044). These changes resulted in a net increase in the number of HER2-positive/ER-negative brain metastases, which more than doubled the proportion of primary breast tumors with this phenotype (26% vs. 11%, respectively; p = 0.08). Additionally, HER2 levels in the primary tumors significantly correlated with overall survival when stratified by ER status (p = 0.011). Conclusions: Brain metastases of breast cancer show significant changes in steroid receptor status and in quantitative HER2 levels compared to matched primary tumors. These data provide a rationale for future studies and may help in designing treatment strategies that target the most likely escape pathways of breast cancer.