Determining a relevant cut-off value when using digital PCR in the assessment of HER2 status in breast tumours

Abstract

Digital PCR (dPCR) is a new technique able to accurately assess the number of copies present of any given gene. The technique produces a numerical value, reflecting the average number of gene copies per cell in approximately 12,000 cells (including both tumour and non-tumour cells). Therefore, regarding its use in HER2 assessment in breast tumours, a well-defined cut off must be established so that the presence of HER2 amplification can be detected in any sample assessed. Here, 48 samples were interrogated by dPCR, all previously assessed by single probe silver in situ hybridisation (SISH) and scored according to the most recent HER2 testing guidelines. HER2 and RNaseP genes were simultaneously assessed in all 48 samples using the QuantStudio digital PCR system (the latter provided the baseline as a non-amplified gene). All the samples that had previously been recorded as not amplified by SISH produced a dPCR value of 3 signals per cell had formerly been reported as HER2 amplified. Evaluation of a significantly larger number of samples must be done to augment this data, however this encouraging early data indicates that further investigation of this technology in the assessment of HER2 status is justified.