In this limited cohort of tissues, the highest frequency of positivity for PD-L1 was observed for lung cancer and H&N cancer, with approximately 18% and 21%, respectively, exhibiting tumour membrane PD-L1 scores greater than or equal to 25% (Figures 1 & 2). Approximately 10% of gastric samples were considered positive for tumour membrane PD-L1, 8% of bladder cancer cases and 2% of colorectal ADC.
When PD-L1 tumour membrane staining greater than 1% is considered positive, then the frequency of positivity increases to 55% for lung cancer, 63% for H&N cancer, 30% for gastric cancer, 23% for bladder cancer and 4% for colorectal adenocarcinoma.
A cut-off of ≥ 25% tumour membrane PD-L1 was applied to define positivity. All paired tissues were then scored positive (≥ 25%) or negative (< 25%). Cases were recorded as non-concordant where the paired tissue outcome of positive or negative did not correlate. Concordance between the scores for each pair of blocks from the same tumour, or for primary versus synchronous metastases, can be viewed in the graphs displayed in Figures 1 and 2, respectively. Details for the non-concordant cases are summarised in Tables 1 and 2).
As summarised in Table 1, for lung carcinoma, no cases of ADC or SCC exhibited a change in PD-L1 classification when two blocks from the same tumour were evaluated. In gastric ADC we recorded a change in classification in 4 out of 53 cases, and for CRC ADC we found a difference between the two blocks evaluated in just 1 of the 55 cases. For bladder carcinoma, 1 out of 55 cases was non-concordant. For the remaining tumour cohorts (4 H&N SCC and 3 pancreatic ADC) 100% concordance was observed between two blocks from the same tumour. Evaluation of primary tumours and synchronous metastasis revealed no differences in PD-L1 scores for the 21 cases of lung carcinoma (Table 2). In the 30 gastric ADC cases, there was a discordant PD-L1 expression score for two pairs of tumours. Similarly, 1 of 55 colorectal ADC examined revealed a primary tumour PD-L1 score of 50% while the metastatic tissue was negative. One out of 15 H&N SCC cases was non-concordant.