Table 3 Preanalytic factors

Tissue thickness

NSCLC and HNSCC tissues sectioned at various thicknesses (3, 4, 5, 6, and 7 μm)

Antibody demonstrated appropriate staining across all thicknesses tested and was representative of clinical PD-L1 status for each case

Tissue fixation

Tonsil cases processed in 10 % NBF, zinc formalin, 95 % alcohol, AFA, Z5 and Prefer with multiple timepoints (1, 6, 12, 24, and 72 h) in each fixative

Timepoints (6, 12, 24, and 72 h) in 10 % NBF, zinc formalin and Z5 were acceptable; 95 % alcohol, AFA and Prefer were not acceptable

Ischemia

KARPASS 299 xenograft tissues with multiple cold ischemia times (0, 0.5, 1, 2, 6, and 24 h)

No significant change in staining intensity from time 0 to hour 24

Cut-slide stability

Four tissue samples; cut at 4 μm and stored at 2–8 and 30 °C. Stained at the Day 0 timepoint and at Day 3 and 14 and monthly Month 1 to 12 timepoints

Staining results at different storage temperatures and at timepoints Day 3 and 14, and Months 1 to 12 consistent with results achieved on Day 0