Exploration of the Tumour Biological Significance of PCLO in Gastric Cancer: Results from a Large Central European Cohort.

Introduction: A recent multiregional whole-exome sequencing of 48 tumour samples from 9 gastric adenocarcinomas discovered PCLO mutations in 23 (47.9%) tumour samples. Based on that unexpected high prevalence of PCLO mutations, we hypothesized a tumour biological significance of PCLO in gastric cancer (GC).

Methods: Tumour samples (whole tissue sections) obtained from 466 patients resected for therapy-naive GC were stained with an anti-PCLO antibody. The histoscore for tumour cells and the presence of immunostaining of stromal cells and tumour vessels was documented for each case. An algorithm for PCLO immunopositivity was formed and correlated with clinicopathological patient characteristics.

Results: 175 GCs were classified as PCLO positive within tumour cells, and 291 as negative. Stromal cells were positive for PCLO in 106 cases and tumour vessels in 84. PCLO-positive GCs more often showed an intestinal phenotype, a lower T category and were more commonly associated with Helicobacter pylori infection. A separate analysis of PCLO expression in intestinal and diffuse type GCs, respectively, showed no significant correlations. Patients with PCLO negative/low tumour cells showed a shortened overall (14.0 ± 1.4 vs. 16.0 ± 1.8 months) and tumour-specific survival (15.0 ± 1.6 months vs. 17.9 ± 3.6). Comparison of PCLOs genotype with its phenotype in 48 tumour samples obtained from nine cases showed no direct correlations with missense mutations.

Conclusion: Our data provide evidence that PCLO is differentially expressed in GC and might delay tumour progression.