HER2DX in HER2-positive inflammatory breast cancer: correlative insights and comparative analysis with...

The HER2DX assay predicts long-term prognosis and pathologic complete response (pCR) in patients with early-stage human epidermal growth factor receptor 2 (HER2)-positive breast cancer receiving neoadjuvant systemic therapy but has not been evaluated in inflammatory breast cancer (IBC).

HER2DX was analyzed in baseline biopsy tissues from 23 patients with stage III HER2-positive IBC on a phase II trial (NCT01796197) treated with neoadjuvant trastuzumab, pertuzumab, and paclitaxel (THP). To assess the assay's predictive accuracy for pCR in IBC, clinical-pathological features and outcomes from this IBC cohort were compared with 156 patients with stage III HER2-positive non-IBC from four different cohorts. Comparative analyses included HER2DX scores, gene signatures, and expression of individual genes between patients with IBC and non-IBC.

Notable differences in clinicopathological characteristics included higher pertuzumab and chemotherapy usage and lower axillary burden in patients with IBC compared with non-IBC. In the combined cohort (n = 179), HER2DX pCR score and pertuzumab use were significant predictors of pCR, but not IBC status. The pCR rates in patients treated with trastuzumab-based chemotherapy (including IBC and non-IBC) were 68.9%, 58.5%, and 16.3% in the HER2DX pCR-high, -medium, and -low groups, respectively. Comparative gene expression analysis indicated minor differences between IBC and non-IBC affecting individual HER2, immune, and proliferation genes.

The HER2DX pCR score could predict pCR in stage III HER2-positive IBC following treatment with de-escalated neoadjuvant systemic therapy and in stage III HER2-positive non-IBC. Elevated pCR rates in HER2-positive IBC with high HER2DX pCR scores suggest there may be a role for treatment de-escalation in these patients and confirmatory studies are justified.