HER2 protein overexpression on the cell surface by IHC and/or gene amplification by FISH are standard methods of determining HER2 positivity. However, these methods do not assess pathway activation. CELx is a live cell platform that can measure signal pathway activation (signal positive). We evaluated the feasibility and clinical efficacy of CELx assay in HER2 signal positive, IHC/FISH negative tumors.


This pilot, phase II, single arm, neoadjuvant study (FACT-2) enrolled HER2 signal positive, hormone receptor (HR)-negative or low, HER2/FISH negative early breast cancer patients. Patients first signed a prescreening repeat biopsy consent for assessment via the CELx assay. Signal positive patients were treated for 21 days with single agent neratinib, an anti-HER2 tyrosine kinase inhibitor, followed by a combination of neratinib plus weekly paclitaxel and carboplatin for 12 weeks. MRI’s were performed before and after single agent neratinib. The primary objective was to evaluate pathologic complete response (pCR) rate. Secondary objectives included rate of RCB 0-1, clinical complete response, safety, toxicity and feasibility to real-world application of CELx.


Four out of 12 prescreened patients were HER2-signaling positive. All patients were female, 75% African Americans and 25% non-Hispanic white. All patients completed the initial 3-week treatment with neratinib. One patient (25%) showed a partial response, two (50%) had stable disease, and one (25%) had progression. The study was stopped early due to low enrollment. No pCR or RCB I was found. Two patients had RCB II and one had RCB III. Two cases of grade 3 diarrhea and one case of dose-limiting neutropenia were recorded. No grade 4 events or treatment-related deaths occurred.


High screen failure challenges broad application of this assay. Although low numbers, data was encouraging and warrants further investigation. High minority participation (75%) indicates diversity will participate in clinical trials if engaged.