HER 2 assessment in locally advanced gastric cancer: comparing the results obtained with the use of two primary tumour blocks versus those obtained with the use of all primary tumour blocks

Aims HER 2 is currently the only biomarker used to select eligible patients with advanced gastric cancer ( GC ) for targeted therapy. The aims of this study were to verify the value of dual‐block HER 2 assessment and to explore whether increasing the block number is more beneficial by carrying out a randomized prospective cohort study in which dual‐block and all‐block HER 2 assessment were compared in resected specimens of GC . Methods and results Five hundred and forty‐nine resected GC specimens were randomly enrolled into two cohorts: a dual‐block group ( n = 274) with two primary tumour blocks tested, and an all‐block group ( n = 275) with all primary tumour blocks tested. Immunohistochemical staining of HER 2 was performed. For HER 2‐equivocal (2+) cases, fluorescence in‐situ hybridization ( FISH ) was performed. As compared with single‐block assessment, dual‐block assessment increased the HER 2 immunohistochemistry ( IHC )‐positive (3+) rate. The rate with dual‐block assessment (11.3%) was significantly higher than that with block 1 assessment (8.8%) ( P = 0.016) and block 2 assessment (9.1%) ( P = 0.031). Similarly, all‐block assessment demonstrated a higher HER 2 3+ rate (12.4%) than single‐block assessment (block 1, 6.5%; block 2, 6.2%; block 3, 7.2%; block 4, 8.7%) ( P < 0.05). HER 2 3+ rates of all‐block and dual‐block assessments showed no significant difference ( P = 0.703). After IHC and FISH results had been combined, the HER 2‐positive rate with all‐block assessment (13.5%) was slightly higher than that with dual‐block assessment (12.0%), although the difference was not statistically significant ( P = 0.62). Conclusions Dual‐block immunohistochemical assessment is an effective, practical and economic approach that is suitable for the preliminary screening of HER 2. We recommend that dual‐block HER 2 assessment be routinely performed on resected specimens of GC . All‐block assessment can be a supplement to dual‐block assessment if necessary.