Is HER2-negative breast cancer really negative? Clinical implication of novel assessment method using inPROBE technology.
Authors: Dariusz M. Stencel, Wojciech Polkowski, Andrzej Kurylcio, Przemysław Kopyto, Marcin Staniszewski, Magdalena Staniszewska
Journal: Journal of Clinical Oncology (2024)

e13030 Background: IHC/FISH is currently the gold standard method of HER2 expression assessment on breast cancer (BC) cells. Recent studies regarding HER2-low category show that the semi-quantitative methods are inaccurate. False-negative results may have a negative impact on the prognosis and treatment outcomes. Methods: To determine the correlation between HER2 receptor levels assessed quantitatively with the use of an innovative diagnostic probe and traditional standard IHC/FISH we conducted an interventional, open-label, single-arm safety and efficacy part I/II clinical trial. In total 22 female patients aged 18 to 75 years with BC and known HER2 status were enrolled. We have developed a novel microprobe merging molecular biology with photonics technology for real-time, in vivo assessment of HER2 expression on BC. The concentration of the HER2 was measured using a diagnostic microprobe inserted in the tumor under ultrasound guidance. To assess the optimal puncture site the second probe examination was additionally performed at the same time in the immediate vicinity of the tumor. Results: Finally, 18 pts. were included in statistical analysis (6 pts. with HER2-positive and 12 pts. with HER2-negative BC). Neither baseline patients’ characteristics nor medical history or concomitant medications did include any potential factors that could affects efficacy or safety analysis. The primary endpoint was initial determination of HER2 receptor concentration ranges detected with microprobe corresponding to HER2 receptor status (positive/negative) identified by IHC/FISH. The study met its primary endpoint. Microprobe mean values in tumor ranged between 4.893 (SD ±10.125) (min) and 8.782 (SD ±12.509) (max), with mean value 6.497 (SD ±10.939) for HER2 IHC positive status and between -3.634 (SD ±6.360) (min) and 5.012 (SD ±2.685) (max), with mean value 1.178 (SD ±2.387) for HER2 IHC negative status. The difference was significant with use of Wilcoxon rank sum exact test. i.e. showed lower values for HER2-negative BC than for HER2-positive BC, p=0.041 for min values. For the remaining comparisons the p-values were not statistically significant; however, the analysis detected reasonable numerical tendency toward higher values in HER2-positive BC as compared to HER2-negative BC. It has been confirmed in analysis performed using linear mixed models for repeated measures. We suspect that HER2-negative group is heterogenous and possibly includes patients with truly HER2-negative (0), but also patients with HER2-low, which could falsely overvalue concentrations range in this group. Conclusions: The current standard IHC/FISH method for HER2 expression assessment could be questioned and challenged as too imprecise and advances in targeted therapy may require more detailed technologies. False negative results can have particularly important clinical and prognostic implications. Clinical trial information: NCT05415943 .