Inverse co-variation of circulating PIWIL2 and PIWIL4 in gastric adenocarcinoma: an exploratory ELISA-based study

Gastric cancer is characterized by substantial molecular heterogeneity, and RNA-mediated regulatory mechanisms may contribute to its biological complexity. PIWI-family proteins are central components of the PIWI-interacting RNA pathway, but their circulating patterns in gastric adenocarcinoma remain insufficiently characterized. This study aimed to describe circulating PIWIL1, PIWIL2, and PIWIL4 protein concentrations and explore intra-cohort co-variation patterns in patients with gastric adenocarcinoma without evaluating disease specificity, diagnostic performance, or clinical utility.

In this cross-sectional, targeted ELISA-based exploratory study, circulating PIWIL1, PIWIL2, and PIWIL4 concentrations were quantified in 93 de-identified gastric adenocarcinoma samples. PIWIL1 and PIWIL2 measurements were available for 88 samples, and PIWIL4 measurements were available for 72 samples. Commercial ELISA kits were used according to the manufacturer's instructions, but independent in-house serum validation, including dilution linearity, serum parallelism, matrix-interference testing, intra- and inter-assay precision, and orthogonal protein confirmation, was not performed. Spearman's rank correlation analysis with false discovery rate correction was used to assess exploratory intra-cohort relationships among PIWI-family proteins.

PIWIL1 and PIWIL2 showed relatively stable circulating distributions, whereas PIWIL4 demonstrated pronounced heterogeneity and right-skewness. The most prominent rank-based relationship was an inverse correlation between PIWIL2 and PIWIL4 (Spearman's ρ ≈ -0.53, q < 0.001), based on 72 complete cases. This correlation remained statistically significant in sensitivity analyses using log-transformed data and exclusion of extreme values. No statistically significant correlations were observed between PIWI-family proteins and CEA or CA 19 - 9 after false discovery rate correction. Exploratory TP53 analyses were not central to the primary objective and are reported descriptively; PIWIL2 showed a modest positive correlation with TP53 (Spearman's ρ = 0.33), while PIWIL4 showed a weak positive correlation (ρ = 0.19).

This study identified an inverse rank-based co-variation between circulating PIWIL2 and PIWIL4 concentrations within a de-identified gastric adenocarcinoma cohort. However, this observation should be interpreted strictly as a pre-validation, exploratory ELISA-derived intra-cohort signal. Because the study lacked comparator groups, clinical annotation, tissue-level confirmation, functional assays, orthogonal protein quantification, and independent serum validation of the ELISA measurements, the observed correlation cannot be considered an analytically validated proteomic association. Further studies with confirmed assay linearity, serum parallelism, matrix-interference assessment, between-plate reproducibility, re-assay of high-value samples at appropriate dilutions, and independent analytical confirmation are required before any biological or clinical significance can be attributed to this finding.