HER2 assessment in locally advanced gastric cancer: comparing the results of using 2 primary tumour blocks versus all primary tumour blocks

Abstract

Aims

HER2 is currently the only biomarker used to select eligible patients with advanced gastric cancer (GC) for targeted therapy. To verify the value of dual-block HER2 assessment and to explore whether increasing the block number is more beneficial, we carried out this randomized prospective cohort study by comparing dual-block and all-block HER2 assessment in resected specimens of GC.

Methods and results

549 resected GC specimens were randomly enrolled into two cohorts: a dual-block group (n=274) with two primary tumor blocks tested, and an all-block group (n=275) with all primary tumor blocks tested. Immunohistochemistry (IHC) staining of HER2 was performed. For HER2 equivocal (2+) cases, fluorescence in situ hybridization (FISH) was performed. Compared with single-block assessment, dual-block assessment increased HER2 IHC-positive (3+) rate. The rate of dual-block (11.3%) was significantly higher than that of block 1 (8.8%) (P=0.016) and block 2 (9.1%) (P=0.031). Similarly, all-block assessment demonstrated a higher HER2 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). HER2 3+ rates of all-block and dual-block assessments demonstrated no significant difference (P=0.703). After combining IHC and FISH results, HER2-positive rate of all-block assessment (13.5%) was slightly higher than that of dual-block assessment (12.0%) without statistical significance (P=0.62).

Conclusions

Dual-block IHC assessment is an effective, practical and economical approach suitable for the preliminary screening of HER2. We recommend that dual-block HER2 assessment be routinely performed on resected specimens of GC. All-block assessment can be a supplement to dual-block assessment if necessary.

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