Effects of Decalcifying Agents of Variable Duration on PD-L1 Immunohistochemistry.

OBJECTIVES: To evaluate the effects of decalcifying agents on programmed cell death ligand 1 (PD-L1) immunohistochemistry (IHC). METHODS: Fragments of 10 placentas (high PD-L1 expressor) and 10 lungs (lower PD-L1 expressor) were formalin-fixed and subjected to four decalcifying solutions (EDTA, formic acid/MasterCal IM Plus [FA/MC], 12% HCl, and Decal STAT/23% HCl) for 1, 2, 6, or 24 hours. H&E staining and PD-L1 using IHC 22C3 pharmDx were performed, and PD-L1 staining was assessed. RESULTS: Minimal to no change in staining intensity or proportion of stained cells was seen with EDTA or FA/MC at all decalcifying durations. Both HCl-based decalcifiers demonstrated a progressive decrease in percentage of positive cells and staining intensity with longer decalcifying duration, particularly with Decal STAT. CONCLUSIONS: EDTA and FA/MC have little effect on PD-L1 expression. 12% HCl causes a progressive decline in staining. Decal STAT dramatically reduced staining with all treatment durations, especially at 24 hours.

Comparison of Dako HercepTest and Ventana PATHWAY Anti-HER2 (4B5) Tests and Their Correlation With Fluorescent In Situ Hybridization in Breast Carcinoma.

OBJECTIVES: We compared the performance of two Food and Drug Administration-approved HER2 immunohistochemistry (IHC) tests: HercepTest (Dako) and PATHWAY anti-HER2 (4B5) (Ventana). MATERIALS AND METHODS: In total, 180 invasive breast carcinomas previously tested by both HercepTest and fluorescent in situ hybridization (FISH) were retested with 4B5. Three pathologists scored the HER2 IHC using the 2013 American Society of Clinical Oncology/College of American Pathologists guidelines. The HER2 IHC results were correlated with FISH. RESULTS: Among 135 equivocal cases by HercepTest, 100 (74.1%) were negative by 4B5. Among 45 positive HercepTest cases 9 (20%) were equivocal by 4B5. Among 135 equivocal HercepTest results, 100 (74.1%) were nonamplified, 18 (13.3%) equivocal, and 17 (12.6%) amplified by FISH. Among the 45 positive results with HercepTest, 2 (4.5%) were nonamplified and 1 (2.2%) was equivocal by FISH. All 37 positive and 3 negative by 4B5 cases were amplified by FISH. The absolute interobserver agreement was high for both tests (Fleiss kappa=0.838 for HercepTest and 0.771 for 4B5). CONCLUSIONS: PATHWAY anti-HER2 (4B5) significantly reduced the number of equivocal results that require additional testing. Although HercepTest was positive in a small number of HER2 nonamplified cases, 4B5 failed to detect 3 cases that were interpreted as positive by FISH, all with nonclassic or low levels of amplification.